[archiso] Create /etc/mtab as symlink.

This is now supported since util-linux pkg enable it.

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

archiso/mkarchiso

@@ -201,9 +201,9 @@ _cleanup () {
     if [[ -d "${work_dir}/root-image/tmp" ]]; then
         find "${work_dir}/root-image/tmp" -mindepth 1 -delete
     fi
-    # Delete etc/mtab if not is a symlink.
+    # Create etc/mtab if not is a symlink.
     if [[ ! -L "${work_dir}/root-image/etc/mtab" ]]; then
-        rm -f "${work_dir}/root-image/etc/mtab"
+        ln -sf "/proc/self/mounts" "${work_dir}/root-image/etc/mtab"
     fi
 }