Block Storage API mv 3.66 enables snapshots of in-use volumes
without requiring a 'force' flag.  For backward compatibility,
the API silently accepts force=true, even though the 'force' flag
is considered invalid for that call.  That behavior is replicated
in the client, where --force with a true value is silently accepted.
The --force option is not advertised in the shell and an option
value that doesn't evaluate to true raises an UnsupportedAttribute
error.  Similar behavior from the v3 Snapshot class, except it
raises a ValueError under similar circumstances.

Change-Id: I7408d0e3a5ed7f4cbcaf65cf3434ad60aaed511d

Remove all cinderclient.v2 classes, mostly incorporating them into
their v3 counterparts and updating the tests and test fixtures.

Depends-on: https://review.opendev.org/c/openstack/horizon/+/800814

Change-Id: I335db5c1799edb2273bf8bfc9e1bc9de404a4ba5

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