Adds tests for compute snapshots API

Adds compute API tests for create, delete, show, and list
snapshots. Also corrects max_microversion for compute/test_volume_rbac
to 2.38 and changes test class name to follow Patrole class naming
conventions (include min_microversion in class name).

Change-Id: Ie04dfa26f598a818dfc3d6eb440dec3e29c5b604
Closes-Bug: #1692173
2 files changed