fw/b UserManagerService: Use ro.build.date to signal upgrades

*) We changed PackageManagerService to use Build.DATE instead of
   Build.FINGERPRINT to detect upgrade.  Do the same for
   UserManagerService.

*) Affects generation of preboot intent and app data migration.

Change-Id: I56887b7ca842afdcf3cf84b27b4c04667cf43307
2 files changed