Migrate test_snapshot_pattern to tempest client

Migrate the test and along with it migrate all the shared
functions used by the tests from OfficialClienTest to
ScenarioTest,create_server_snapshot()

Change-Id: I4d95cd02fcbbb62bb1631a38ee5d2c7e7d8f8d63
Merge "Migrate test_snapshot_pattern to tempest client"