@classmethod
  def unmount_persistent_disk(cls, host, keyname, is_verbose):
    try:
      remote_output = cls.ssh(host, keyname, 'umount {0}'.format(
        cls.PERSISTENT_MOUNT_POINT), is_verbose)
      AppScaleLogger.verbose(remote_output, is_verbose)
    except ShellException:
      pass
Unmounts the persistent disk that was previously mounted on the named
dataset/ETHPy150Open AppScale/appscale-tools/lib/remote_helper.py/RemoteHelper.unmount_persistent_disk