Clean up servers created in test_multiple_create.py

Now several servers are created in test_multiple_create.py but
the servers are not deleted when the test finishes.
This makes the servers be deleted by fixing the way of
appending them to cls.servers.

Fixes bug: 1171697

Change-Id: Ie6768a6ecafb16e277964ca82201be213f885f4e
Merge "Clean up servers created in test_multiple_create.py"