fence_xvm: remove unused params and expose port (domname)

Not tested.

Remove $fence_xvm_clu_iface/$fence_xvm_clu_network which were not used for anything in this manifest.  Once upon a time, they could be used to derive the pacemaker cluster IP which *was* equivalent to the pacemaker node name which in turn was passed along here: https://github.com/redhat-openstack/astapor/blob/4e4a138288fdaf6336758f3944da4a731571919b/puppet/modules/quickstack/manifests/pacemaker/common.pp#L85 .  This is no longer the case (the pacemaker node name is now an fqdn) and now we can rely on pacemaker::stonith::fence_xvm to derive the pacemaker node name rather than pass it along.

Expose the $fence_xvm_port parameter which corresponds to the vm's dom name or uuid.  If it is not set, continue to make the assumption currently being made, that the fact $::hostname is the dom name.