Merge branch pull request #13551 from pritha-srivastava/wip-rgw-role-tenant

Merge branch pull request #13551 from pritha-srivastava/wip-rgw-role-tenant

rgw: Replaced rgw userid with tenant in ARN for Roles.
rgw: Adding roles under the scope of tenants.
rgw: Added code for Role input validation.
rgw: Added code to fetch a role by its id.
rgw: Added code to allow tenant name as part of role name also.
rgw: Better reporting of missing input values in case of radosgw-admin
     commands for Roles.

Reviewed-By: Adam C. Emerson <aemerson@redhat.com>