Ceph used to use port 6789 (no need to specify it), but with the messenger v2
from Ceph it switched to port 3300 while 6789 still works.
librados/librbd/libvirt will automatically figure out the ports to use if none is
specified.
Therefor there is no need for CloudStack to explicitely define the port in the XML
passed to Libvirt or Qemu.
Leave blank if no port number has been defined by the user.