overlay/05core: ship by-id/coreos-boot-disk udev rule in initrd only

The associated script only exists in the initrd. But also, we only need
the symlink in the initrd anyway.

Fixes 6d7b9ad ("overlay.d: add udev rule for creating stable symlink to
boot disk").

Fixes openshift/os#755.

Author: jlebon

overlay.d/05core/usr/lib/udev/rules.d/80-coreos-boot-disk.rules overlay.d/05core/usr/lib/dracut/modules.d/35coreos-ignition/80-coreos-boot-disk.rules

@@ -31,7 +31,8 @@ install() {
     inst_script "$moddir/coreos-gpt-setup.sh" \
         "/usr/sbin/coreos-gpt-setup"
 
-    inst_simple "/usr/lib/udev/rules.d/80-coreos-boot-disk.rules"
+    inst_simple "$moddir/80-coreos-boot-disk.rules" \
+        "/usr/lib/udev/rules.d/80-coreos-boot-disk.rules"
 
     inst_script "$moddir/coreos-disk-contains-fs.sh" \
         "/usr/lib/udev/coreos-disk-contains-fs"