Simplify role addtion helper functions

Because adding the role is idempotent, we can save doing the initial
check for role assignment.  Also simplify the output matching by using
osc's filters where appropriate.

Co-Authored-By: Jens Harbott <harbott@osism.tech>
Change-Id: If2a661cc565a43a7821b8f0a10edd97de08eb911
1 file changed