Add metric to measure duration of resolving request pool

This will help us identify if the calls to Hadoop libraries for resolving the
request pool and checking access are slow.

Change-Id: Id89bdcedf91758994b2cd1ef93f30e04ef90e242
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5198
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: jenkins