tmpfiles: silently ignore any path that passes through autofs (#6506)

tmpfiles: silently ignore any path that passes through autofs (#6506)

If a path passes though an autofs filesystem, then accessing
the path might trigger and automount.  As systemd-tmpfiles is run before
the network is up, and as automounts are often used for networked
filesystems, this can cause a deadlock.

So chase_symlinks is enhance to accept a new flag which tells it
to check for autofs, and return -EREMOTE if autofs is found.

tmpfiles is changed to check just before acting on a path so that it
can avoid autofs even if a symlink was created earlier by tmpfiles
that would send this path through an autofs.

This fixes a deadlock that happens when /home is listed in /etc/fstab as
x-systemd.automount for an NFS directory.