Also removes the v2 support from the generic client and restores a
skipped test.
Additionally, the cinderclient.tests.v2.test_availablity_zone module
depends on the v2.shell class, so move that module to v3, update the
v3 AvailablityZone class, and make appropriate adjustments to the
tests and test fixtures.
Change-Id: I7a3cca15f5944141d510a75af6684221c297963b