user-or-group-id is optional for permission-set.

When type is 'user' user_or_group_id is context.user_id by default.
Removed duplicated cinder/v2/volume_acl.py, cinder/v1 has the same
volume_acl.

Change-Id: Id7e399b2ee815ac0d30cf04ba89901f423d3b98d