lttng module failed to build on Bionic 4.18 Azure

[Po-Hsu Lin]

For Azure Bionic 4.18 kernel, the result is differ from 1802443

 Building initial module for 4.18.0-1004-azure
 ERROR (dkms apport): kernel package linux-headers-4.18.0-1004-azure is not supported
 Error! Bad return status for module build on kernel: 4.18.0-1004-azure (x86_64)
 Consult /var/lib/dkms/lttng-modules/2.10.5/build/make.log for more information.
 Setting up build-essential (12.4ubuntu1) ...
 Setting up gcc-multilib (4:7.3.0-3ubuntu2.1) ...
 Processing triggers for libc-bin (2.27-3ubuntu1) ...
 Processing triggers for ureadahead (0.100.0-20) ...
 Processing triggers for systemd (237-3ubuntu10.6) ...
 W: --force-yes is deprecated, use one of the options starting with --allow instead.
 Running 'which gcc'
 /usr/bin/gcc
 Running 'dkms status -m lttng-modules | grep installed'
 Running 'cat /var/lib/dkms/lttng-modules/*/build/make.log'
 DKMS make.log for lttng-modules-2.10.5 for kernel 4.18.0-1004-azure (x86_64)
 Wed Nov 14 08:44:17 UTC 2018
 make: Entering directory '/usr/src/linux-headers-4.18.0-1004-azure'
 make: Makefile: No such file or directory
 make: *** No rule to make target 'Makefile'. Stop.
 make: Leaving directory '/usr/src/linux-headers-4.18.0-1004-azure'

 Exception escaping from test:
 Traceback (most recent call last):
 File "/home/azure/autotest/client/shared/test.py", line 387, in _exec
 *p_args, **p_dargs)
 File "/home/azure/autotest/client/shared/utils.py", line 865, in update_version
 install(*args, **dargs)
 File "/home/azure/autotest/client/tests/ubuntu_lttng_smoke_test/ubuntu_lttng_smoke_test.py", line 58, in setup
 raise error.TestError('DKMS failed to install')
 TestError: DKMS failed to install

[Po-Hsu Lin (cypressyew)]

Module build OK with newer kernel.