[init] trigger late_start on property change

Android's late_start is triggered by mount_all, which also determines whether
the /data partition is encrypted.

Mer rootfs now has to spawn a service after mount points are ready, and before
peripheral services (such as sensors, wlan, bt, ...) are started. That service
has to issue `setprop droid.late_start trigger_late_start`

Change-Id: I3a2c118e671b9eae8e8f1cb64f55da57c214ac8f
Signed-off-by: Simonas Leleiva <simonas.leleiva@jollamobile.com>
Merge pull request #4 from sledges/late-start

[init] trigger late_start on property change