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.

Example output for CentOS:

    # ceph-deploy mon create node2
    [ceph_deploy.mon][DEBUG ] Deploying mon, cluster ceph hosts node2
    [ceph_deploy.mon][DEBUG ] detecting platform for host node2 ...
    [ceph_deploy.mon][INFO  ] distro info: CentOS 6.4 Final
    [node2][DEBUG ] deploying mon to node2
    [node2][DEBUG ] remote hostname: localhost
    [node2][DEBUG ] checking for done path: /var/lib/ceph/mon/ceph-localhost/done
    [node2][INFO  ] create a done file to avoid re-doing the mon deployment
    [node2][INFO  ] create the init path if it does not exist
    [node2][INFO  ] locating `service` executable...
    [node2][INFO  ] found `service` executable: /sbin/service
    [node2][INFO  ] Running command: /sbin/service ceph start mon.localhost
    [node2][INFO  ] === mon.localhost ===
    [node2][INFO  ] Starting Ceph mon.localhost on localhost...
    [node2][INFO  ] Starting ceph-create-keys on localhost...


[0] http://tracker.ceph.com/issues/5839