compute: Move device tagging tests to use wait_until=SSHABLE
compute: Move device tagging tests to use wait_until=SSHABLE

Waiting until the test instance is SSH-able before continuing
the test will help us avoid failures to detach a volume from
server, more info in the related bug.

Related-Bug: #1960346

Change-Id: Id5496572ce6cef06e71bae1a1040b274bacf4f79

openstack/tempest,openstack/tempest