Add ConsistencyGroup Exceptions in tempest

The exceptions ConsistencyGroupException and
ConsistencyGroupSnapshotException are required by
cinder-tempest-plugin[1][2] when the
CG or CG Snapshot fails to create and is in error state.
These exceptions never existed as part of the original topic[3]
but failures are seen while running tests as reported in the bug.

[1] https://github.com/openstack/cinder-tempest-plugin/blob/master/cinder_tempest_plugin/services/consistencygroups_client.py#L140
[2] https://github.com/openstack/cinder-tempest-plugin/blob/master/cinder_tempest_plugin/services/consistencygroups_client.py#L172
[3] https://review.opendev.org/#/q/topic:cg-tests+(status:open+OR+status:merged)

Change-Id: I62e0ba556b884c94f6e8796a2e6f6d8083277fa4
Closes-Bug: #1858417
2 files changed