Update /v1/rbac/roles API endpoint to include corresponding permission grant objects.
Update /v1/rbac/roles API endpoint to include corresponding permission
grant objects.

This makes the output more useful since user doesn't need to query for
permission grants separately.

tonybaloney/st2,StackStorm/st2,tonybaloney/st2,Plexxi/st2,StackStorm/st2,Plexxi/st2,tonybaloney/st2,nzlosh/st2,Plexxi/st2,Plexxi/st2,StackStorm/st2,nzlosh/st2,nzlosh/st2,nzlosh/st2,StackStorm/st2