fence_xvm updates

Sample usage:

  class {'pacemaker::stonith::fence_xvm':
    name              => "$::hostname",
    manage_key_file   => true,
    key_file_password => '123456788888',
  }

  class {'pacemaker::stonith::fence_xvm':
    name             => "$::hostname",
    manage_key_file  => false,
    port             => "$::hostname",    # the name of the vm
    pcmk_host        => $clu_ip_address,  # the hostname or IP that pacemaker uses
  }