Waiting for ACTIVE state in rescue tests

The v2 test_server_rescue.py is waited for ACTIVE state before
executing the test cases, but the test_server_rescue_negative.py
not. It is possible the first server not reaches the active state
even if the second server went through BUILD->ACTIVE->RESCUE state in
parallel.

* Ensure the fist server is in the ACTIVE state.

Closes-Bug: #1301832

Change-Id: I900c3d6e1eac399ba6c6e13c302b927bcd6929e7
Merge "Waiting for ACTIVE state in rescue tests"