feat(squash): install umount util

Also install umount binary, make it possible to cleanup squash overlay
mounts. This is useful for other tools reusing the dracut initramfs built
with squash module enabled.

Signed-off-by: Kairui Song <kasong@redhat.com>

modules.d/99squash/module-setup.sh

@@ -42,11 +42,11 @@ installpost() {
     # Install required modules and binaries for the squash image init script.
     if [[ $_busybox ]]; then
         inst "$_busybox" /usr/bin/busybox
-        for _i in sh echo mount modprobe mkdir switch_root grep; do
+        for _i in sh echo mount modprobe mkdir switch_root grep umount; do
             ln_r /usr/bin/busybox /usr/bin/$_i
         done
     else
-        DRACUT_RESOLVE_DEPS=1 inst_multiple sh mount modprobe mkdir switch_root grep
+        DRACUT_RESOLVE_DEPS=1 inst_multiple sh mount modprobe mkdir switch_root grep umount
     fi
 
     hostonly="" instmods "loop" "squashfs" "overlay"