This helper uses other binaries (like awk), which can fail or be killed.
It this case might be, that no mountpoint is found.
Or, on other hand, the whole mount point path is wrong, and is absend in
mountinfo.
Return explicit error in this case.
Without this patch, script will proceed further, and, since returned value is
empty, it doesn't equal to "autofs", so script will try to bind-mount autofs
mount, resulting in hung.

 travis-ci: success for systemd-autofs-restart.sh: explicitly return result from get_fs_type
Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>