Switch test_snapshot_pattern to full image

Use full based ubuntu image for tests with snapshot. Cirros has issues
in self written cloudinit which cleanup authorized_keys on second run
after server is build from snapshot and uuid is changed.

Add the following options
* image_full_ref
* image_full_username
* image_full_flavor

Related-Prod: PRODX-27524
Change-Id: I632829ad1bbed8f0c666b2f1488e078f262dfb7c
(cherry picked from commit d015caba5149a986c8fb1bbebe5f3a7fd6eec71e)
2 files changed