Fix occasional admission control test failures

The admission control tests could occasionally fail when cancelled
queries return OK (IMPALA-1047). Until fixed, we can just treat
such queries as if there were cancelled.

Change-Id: Id9fc8e9f585e466059d4ffefb4d9ed407206ad1d
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3019
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins