init: avoid add root dev to fstab for vm image

This was erroneously added to overly broad class of images.

features.in/init/rootfs/image-scripts.d/90-systemd

@@ -19,7 +19,3 @@ sub /etc/initrd.mk 'MODULES_PRELOAD += autofs4'
 
 # don't allow systemd to set LANG (see also #27408)
 sub /etc/locale.conf 'LANG='
-
-# aufs2 root is rw in reality; but don't bother if there's a record already
-grep -q '[[:space:]]/[[:space:]]' /etc/fstab ||
-	sub /etc/fstab '/dev/root / auto defaults 0 0'

features.in/init/stage2/image-scripts.d/91-systemd

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+# the part below relates to systemd as init specifically
+rpm -q systemd-sysvinit || exit 0
+
+sub() {
+	local file="$1"
+	shift
+	for i in "$@"; do
+		grep -q "^$i" "$file" || echo "$i" >> "$file"
+	done
+}
+
+# aufs2 root is rw in reality; but don't bother if there's a record already
+grep -q '[[:space:]]/[[:space:]]' /etc/fstab ||
+	sub /etc/fstab '/dev/root / auto defaults 0 0'