Allow /query_summary to be run while query is running.

The exec summary on that page dynamically updates and is useful to see what
is the progress of the query.

Change-Id: I04542426d80091ff2bd4f59e39f126e59ae32e91
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5097
Tested-by: jenkins
Reviewed-by: Nong Li <nong@cloudera.com>
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5256