[CDH5] Update grant/revoke tests to drop any roles granted to current user before running

Change-Id: Iba03654f56144cb849267520b82a951a29f0dfb2
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4324
Reviewed-by: Lenni Kuff <lskuff@cloudera.com>
Tested-by: jenkins