shutdown: fix PATH

Some systems might not use /bin:/sbin in their paths anymore, but we're
still using it in initramfs, so make sure our PATH is correct.

modules.d/99shutdown/shutdown.sh

@@ -10,6 +10,7 @@
 #!/bin/sh
 . /lib/dracut-lib.sh
 export TERM=linux
+PATH=/usr/sbin:/usr/bin:/sbin:/bin
 
 emergency_shell()
 {