message: nydusd: fix is_mount failure
  `is_mount` can only take a canonicalized path which is shown in
  /proc/self/mounts.
diff: @@ -401,7 +401,8 @@ pub fn create_nydus_daemon(
  mount_cmd: Option<FsBackendMountCmd>,
  bti: BuildTimeInfo,
  ) -> Result<Arc<dyn NydusDaemon + Send + Sync>> {
  - let session = FuseSession::new(Path::new(mountpoint), "rafs", "", readonly)?;
  + let mnt = Path::new(mountpoint).canonicalize()?;
  + let session = FuseSession::new(&mnt, "rafs", "", readonly)?;
  // Create upgrade manager
  let upgrade_mgr = supervisor
  @@ -439,9 +440,7 @@ pub fn create_nydus_daemon(
  // Without api socket, nydusd can't do neither live-upgrade nor failover, so the helper
  // finding a victim is not necessary.
  - if (api_sock.as_ref().is_some()
  - && !upgrade
  - && !is_crashed(mountpoint, api_sock.as_ref().unwrap())?)
  + if (api_sock.as_ref().is_some() && !upgrade && !is_crashed(&mnt, api_sock.as_ref().unwrap())?)
  || api_sock.is_none()
  {
  if let Some(cmd) = mount_cmd {
  @@ -451,9 +450,7 @@ pub fn create_nydus_daemon(
  daemon
  .on_event(DaemonStateMachineInput::Mount)
  .map_err(|e| eother!(e))?;
  - daemon
  - .conn
  - .store(calc_fuse_conn(mountpoint)?, Ordering::Relaxed);
  + daemon.conn.store(calc_fuse_conn(mnt)?, Ordering::Relaxed);
  }
  Ok(daemon)
  