Ensure lazy translation is disabled properly

Ensure lazy translation is disabled properly

Commit 894f20d9cf57b36ccf9a675c6b2b070d56c9b297 changed the way that
enable_lazy() is being configured in cinder's test cases.  The changes
were required to remove the use of _lazy from the oslo's i18n library.
_lazy was removed from i18n and the code that was accessing the internal
variable broke.  The commit referenced above made changes to remove
the use of _lazy.

The commit, however, changed the behavior of the test cases to only
enable_lazy without disabling it, which diverges from the original
behavior.

This commit uses the new oslo.i18n ToggleLazy fixture (added in 1.3.0).

Closes-bug: 1408099
Change-Id: If9530b2bb8f0f511ccff4527ea9f2d13f7103bdb