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

[hoonetorg]

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.

[hoonetorg]

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