systemd-autofs-restart.sh: fix error handling in case of system limitation

Without this patch any error in check_fs_type function is considered as a
grant to process to bind-mount.
This patch splits mount point fs type discovering and comparison to autofs
type, thus allowing to check for discovery errors.

Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>