use optparse instead of arg_parse cbvdiff for compatibility

Change-Id: I604354823c71b91a167646c01e2bb6ea9d8c8822
Reviewed-on: http://review.couchbase.org/41752
Tested-by: Sundararaman Sridharan <sundar@couchbase.com>
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>