Check server terminations on "delete server" tests

Current "delete server" tests check the API response code only
and do not check server terminations. In current tests, Tempest
cannot detect the termination errors even if they happen.
This patch adds the checks for these tests.

Change-Id: Ib9ba09e86819d7f1027c90cf3ca98dee350125e8
Merge "Check server terminations on "delete server" tests"