Fix assertion while waiting for ACTIVE status

Reasons:
 - For certain reasons Cassandra instances are in
   SHUTDOWN state for short period of time, and it's breaks
   assertion in test that waiting for guest to become active.

Changes:
 - fixing assertion from expecting only BUILD state to expect one of:
   "BUILD" or "SHUTDOWN".

Change-Id: I6009e4c0979abb9a469aed4d3cf2b0f53df4c046
Partial-Bug: #1314980