overlay: mount-android.conf: emit mounted-android signal

See https://gitlab.com/ubports/core/rootfs-builder-debos/-/merge_requests/23

overlay/system/etc/init/mount-android.conf

@@ -5,6 +5,8 @@ description "Mount device partitions"
 start on (startup
     and started udev)
 
+emits mounted-android
+
 task
 
 script
@@ -22,5 +24,6 @@ script
     if [ -d /android/metadata ]; then
         mount -o bind /android/metadata /var/lib/lxc/android/rootfs/metadata
     fi
+    initctl emit -n mounted-android
 end script