After manually install the pkg-config package on the host with :

-> apt-get install pkg-config

Another error occurs (python_venv_build.log) :

2020-07-08T10:13:25,242 Building wheels for collected packages: libvirt-python
2020-07-08T10:13:25,243   Created temporary directory: /tmp/pip-wheel-vpksdxua
2020-07-08T10:13:25,243   Building wheel for libvirt-python (setup.py): started
2020-07-08T10:13:25,243   Destination directory: /tmp/pip-wheel-vpksdxua
2020-07-08T10:13:25,243   Running command /openstack/venvs/masakari-20.1.2/bin/python3 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"'; __file__='"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /tmp/pip-wheel-vpksdxua --python-tag cp36
2020-07-08T10:13:25,503   Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:25,503   Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:25,503   to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:25,504   No package 'libvirt' found
2020-07-08T10:13:25,507   Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:25,507   Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:25,507   to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:25,507   No package 'libvirt' found
2020-07-08T10:13:25,549   running bdist_wheel
2020-07-08T10:13:25,553   running build
2020-07-08T10:13:25,553   /usr/bin/pkg-config --print-errors --atleast-version=0.9.11 libvirt
2020-07-08T10:13:25,557   Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:25,558   Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:25,558   to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:25,558   No package 'libvirt' found
2020-07-08T10:13:25,558   error: command '/usr/bin/pkg-config' failed with exit status 1
2020-07-08T10:13:25,586   Building wheel for libvirt-python (setup.py): finished with status 'error'
2020-07-08T10:13:25,587   ERROR: Failed building wheel for libvirt-python
2020-07-08T10:13:25,587   Running setup.py clean for libvirt-python
2020-07-08T10:13:25,587   Running command /openstack/venvs/masakari-20.1.2/bin/python3 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"'; __file__='"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' clean --all
2020-07-08T10:13:25,849   Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:25,850   Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:25,850   to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:25,850   No package 'libvirt' found
2020-07-08T10:13:25,854   Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:25,854   Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:25,854   to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:25,854   No package 'libvirt' found
2020-07-08T10:13:25,884   running clean
2020-07-08T10:13:25,884   'build/lib.linux-x86_64-3.6' does not exist -- can't clean it
2020-07-08T10:13:25,884   'build/bdist.linux-x86_64' does not exist -- can't clean it
2020-07-08T10:13:25,884   'build/scripts-3.6' does not exist -- can't clean it
2020-07-08T10:13:25,884   removing 'build'
2020-07-08T10:13:25,908 Failed to build libvirt-python
2020-07-08T10:13:25,939 Installing collected packages: libvirt-python, masakari-monitors
2020-07-08T10:13:25,939   Created temporary directory: /tmp/pip-record-ifkp__mi
2020-07-08T10:13:25,940     Running setup.py install for libvirt-python: started
2020-07-08T10:13:25,940     Running command /openstack/venvs/masakari-20.1.2/bin/python3 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"'; __file__='"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-ifkp__mi/install-record.txt --single-version-externally-managed --compile --install-headers /openstack/venvs/masakari-20.1.2/include/site/python3.6/libvirt-python
2020-07-08T10:13:26,201     Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:26,201     Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:26,201     to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:26,201     No package 'libvirt' found
2020-07-08T10:13:26,205     Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:26,205     Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:26,205     to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:26,205     No package 'libvirt' found
2020-07-08T10:13:26,240     running install
2020-07-08T10:13:26,242     running build
2020-07-08T10:13:26,242     /usr/bin/pkg-config --print-errors --atleast-version=0.9.11 libvirt
2020-07-08T10:13:26,246     Package libvirt was not found in the pkg-config search path.
2020-07-08T10:13:26,246     Perhaps you should add the directory containing `libvirt.pc'
2020-07-08T10:13:26,246     to the PKG_CONFIG_PATH environment variable
2020-07-08T10:13:26,246     No package 'libvirt' found
2020-07-08T10:13:26,246     error: command '/usr/bin/pkg-config' failed with exit status 1
2020-07-08T10:13:26,278     Running setup.py install for libvirt-python: finished with status 'error'
2020-07-08T10:13:26,279 Cleaning up...
2020-07-08T10:13:26,279   Removing source in /tmp/pip-install-ei67pgjj/libvirt-python
2020-07-08T10:13:26,291 Removed build tracker '/tmp/pip-req-tracker-osylkink'
2020-07-08T10:13:26,291 ERROR: Command errored out with exit status 1: /openstack/venvs/masakari-20.1.2/bin/python3 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"'; __file__='"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-ifkp__mi/install-record.txt --single-version-externally-managed --compile --install-headers /openstack/venvs/masakari-20.1.2/include/site/python3.6/libvirt-python Check the logs for full command output.
2020-07-08T10:13:26,291 Exception information:
2020-07-08T10:13:26,291 Traceback (most recent call last):
2020-07-08T10:13:26,291   File "/openstack/venvs/masakari-20.1.2/lib/python3.6/site-packages/pip/_internal/cli/base_command.py", line 153, in _main
2020-07-08T10:13:26,291     status = self.run(options, args)
2020-07-08T10:13:26,291   File "/openstack/venvs/masakari-20.1.2/lib/python3.6/site-packages/pip/_internal/commands/install.py", line 454, in run
2020-07-08T10:13:26,291     use_user_site=options.use_user_site,
2020-07-08T10:13:26,291   File "/openstack/venvs/masakari-20.1.2/lib/python3.6/site-packages/pip/_internal/req/__init__.py", line 62, in install_given_reqs
2020-07-08T10:13:26,291     **kwargs
2020-07-08T10:13:26,291   File "/openstack/venvs/masakari-20.1.2/lib/python3.6/site-packages/pip/_internal/req/req_install.py", line 888, in install
2020-07-08T10:13:26,291     cwd=self.unpacked_source_directory,
2020-07-08T10:13:26,291   File "/openstack/venvs/masakari-20.1.2/lib/python3.6/site-packages/pip/_internal/utils/subprocess.py", line 275, in runner
2020-07-08T10:13:26,291     spinner=spinner,
2020-07-08T10:13:26,291   File "/openstack/venvs/masakari-20.1.2/lib/python3.6/site-packages/pip/_internal/utils/subprocess.py", line 242, in call_subprocess
2020-07-08T10:13:26,291     raise InstallationError(exc_msg)
2020-07-08T10:13:26,291 pip._internal.exceptions.InstallationError: Command errored out with exit status 1: /openstack/venvs/masakari-20.1.2/bin/python3 -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"'; __file__='"'"'/tmp/pip-install-ei67pgjj/libvirt-python/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-ifkp__mi/install-record.txt --single-version-externally-managed --compile --install-headers /openstack/venvs/masakari-20.1.2/include/site/python3.6/libvirt-python Check the logs for full command output.
2020-07-08T10:13:26,366 WARNING: You are using pip version 19.3; however, version 20.1.1 is available.
2020-07-08T10:13:26,366 You should consider upgrading via the 'pip install --upgrade pip' command.