Comment 1 for bug 1817032

When I revert this commit (https://github.com/openstack/oslo.cache/commit/62b53099861134859482656dc92db81243b88bd9) I obtain the following traceback:

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    b'Traceback (most recent call last):'
    b' File "/tmp/oslo.cache/oslo_cache/tests/test_dict_backend.py", line 37, in setUp'
    b" 'oslo_cache.dict', arguments={'expiration_time': 0.5})"
    b' File "/tmp/oslo.cache/.tox/py37/lib/python3.7/site-packages/dogpile/cache/region.py", line 416, in configure'
    b' backend_cls = _backend_loader.load(backend)'
    b' File "/tmp/oslo.cache/.tox/py37/lib/python3.7/site-packages/dogpile/util/langhelpers.py", line 34, in load'
    b' return self.impls[name]()'
    b' File "/tmp/oslo.cache/.tox/py37/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2410, in load'
    b' self.require(*args, **kwargs)'
    b' File "/tmp/oslo.cache/.tox/py37/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2433, in require'
    b' items = working_set.resolve(reqs, env, installer, extras=self.extras)'
    b' File "/tmp/oslo.cache/.tox/py37/lib/python3.7/site-packages/pkg_resources/__init__.py", line 791, in resolve'
    b' raise VersionConflict(dist, req).with_context(dependent_req)'
    b"pkg_resources.VersionConflict: (dogpile.cache 0.7.1 (/tmp/oslo.cache/.tox/py37/lib/python3.7/site-packages), Requirement.parse('dogpile.cache<0.7.0,>=0.6.2'))"
    b''