Close all queries in test_cancellation

The queries in test_cancellation are currently cancelled but not closed, causing some test
queries to eventually time out because the admission controller limits are passed. This
patch ensures that all queries issued in test_cancellation are closed.

Change-Id: I65b26672155e31889bb6f43d3ac87be0f7b4eb72
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2187
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Tested-by: jenkins