Handle the ring_name variable being none in Ring.__init__

Change-Id: Ifbcf217e525e50f62b98028ed5292be58db64bad
Signed-off-by: Mohammed Junaid <junaid@redhat.com>
Reviewed-on: http://review.gluster.org/5459
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>