Make GetExecSummary() RPC callable while query is running.

Change-Id: I51fbade93b735dc007b1e84762194061a466947a
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4768
Tested-by: jenkins
Reviewed-by: Nong Li <nong@cloudera.com>
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5091