Make fuser command time out

This avoids situations in which fuser hangs because of open files on
remote file systems when the remote system goes down.
I have also passed this bug on to the maintainers of psmisc since it
should really be fixed in fuser.
This is based on a patch submitted by evermind@tuxfamily.org

Reported-by: evermind@tuxfamily.org
X-Gentoo-Bug: 455458
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=455458

sh/rc-mount.sh

@@ -41,7 +41,8 @@ do_unmount()
 		retry=4 # Effectively TERM, sleep 1, TERM, sleep 1, KILL, sleep 1
 		while ! LC_ALL=C $cmd "$mnt" 2>/dev/null; do
 			if type fuser >/dev/null 2>&1; then
-				pids="$(fuser $f_opts "$mnt" 2>/dev/null)"
+				pids="$(timeout -k 10 -s KILL "${rc_fuser_timeout:-60}" \
+					fuser $f_opts "$mnt" 2>/dev/null)"
 			fi
 			case " $pids " in
 				*" $$ "*)