mds.py: make defining addr/port for mds_create optional

It would be nice If running the salt ceph.create_mds module works without defining addr and port of mds.
Also creating the environment file /var/lib/ceph/mds/systemd/ with bind addr/port and ceph cluster name could be optional then.
Defining a port isn't that easy, because I need them in the dynamic range (6800-7200) of the osd's and defining a port there is hard (probably it's already used).
On el7 this file is ignored currently, that's why it works for me.
I'm not sure about SLES.

I'm not sure if sesceph ceph.mds_create must be touched for that?