Add vendor hook after userdata becoming available

The init process provides a vendor hook for dynamically initializing
system properties during early boot. During this hook, however, userdata
may not yet be available if the device is encrypted. Therefore, add an
additional hook here in vold that is triggered once userdata is
available, so that system properties can be set based on data previously
stored on the userdata partition.

Issue: FP2N-386
Change-Id: Ie7aa75d0768489b119ab3da0e1a75e2d90c9dc6b
4 files changed