Migrate `mon create` to the new distro structure

The following changes moves all the `mon create` code to its own distro module [0].

This allows us to not special case every distro when creating mons and have better logging ouput when we are performing remote actions in nodes.

It also fixes a problem that `ceph-deploy mon create` on CentOS does not work because the `service` executable is never found.

[0] http://tracker.ceph.com/issues/5839