Added script to look for merged Gerrit changes that are missing from the repository

Change-Id: Ibf0df17f951beb440f752080bfc2d146ffdef58e
Reviewed-on: http://review.couchbase.org/32672
Reviewed-by: Philip Labee <philip@couchbase.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>