supermin-init-prelude: add timeout on udevadm trigger and make non-fatal

We hit a case on ppc64le where this just hung forever. Let's add a
timeout on it.

And since this is best effort, let's just ignore any errors from the
command. If a symlink is missing, we'll just error out with a clearer
error down the line anyway.

Author: jlebon

src/supermin-init-prelude.sh

@@ -23,7 +23,9 @@ LANG=C /sbin/load_policy  -i
 
 # we want /dev/disk symlinks for coreos-installer
 /usr/lib/systemd/systemd-udevd --daemon
-/usr/sbin/udevadm trigger --settle
+# We've seen this hang before, so add a timeout. This is best-effort anyway, so
+# let's not fail on it.
+timeout 30s /usr/sbin/udevadm trigger --settle || :
 
 # set up networking
 if [ -z "${RUNVM_NONET:-}" ]; then