message: nydus-test: lazy umount
diff: @@ -728,7 +728,7 @@ class NydusDaemon(utils.ArtifactProcess):
  Umount is sometimes invoked during teardown. So it can't assert.
  """
  self._catcher_dead = True
  - ret, _ = utils.execute(["umount", self.mountpoint], print_output=True)
  + ret, _ = utils.execute(["umount", "-l", self.mountpoint], print_output=True)
  assert ret
  # self.p.wait()
  # assert self.p.returncode == 0
  