Add PlanFragmentExecutor counter for time sent in Prepare().
Add PlanFragmentExecutor counter for time sent in Prepare().

Change-Id: I956027a7ca6eb04cb2391da913b51d941de59654
Reviewed-on: http://gerrit.ent.cloudera.com:8080/647
Reviewed-by: Marcel Kornacker <44592b4eea36663c86b994bb0ea99d15309c1c7d@cloudera.com>
Tested-by: jenkins
Reviewed-by: Nong Li <99a5e5f8f5911755b88e0b536d46aafa102bed41@cloudera.com>

michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala