Fix image deletion checks after unshelve server

Tempest test checks and expect image to be deleted immediately
when server is unshelved and in active state. But there is no
guarantee of immediate image deletion from glance side.

API ref does not state anything even it explicitly states
about async postcondition
-https://developer.openstack.org/api-ref/compute/?expanded=unshelve-restore-shelved-server-unshelve-action-detail#unshelve-restore-shelved-server-unshelve-action

Discussed in below mail thread-
- http://lists.openstack.org/pipermail/openstack-dev/2017-June/118574.html

Test should wait for image deletion and if it does not then fail.
Closes-Bug: #1697953

Change-Id: I6552a3e4a7133a9fdaf203ab31cfef6dff764a62
1 file changed