Allow devices to specify certain ro. props via TARGET_UNIFIED_DEVICE

This modifies buildinfo.sh to not set model, name, description, and
fingerprint in build.prop. These can then be set via custom init
lib.
This also fixes ota_from_target_files to function without these
props being preset.

Change-Id: Ia7dfcdea5aab7ebf51d3ab29a0d9e5751fc96663
Merge remote-tracking branch 'upstream/android-4.4' into android-4.4

Conflicts:
	core/Makefile
	tools/releasetools/ota_from_target_files

Change-Id: I7a3bac75468ced5f216f6af8d8dd0ee525e4a101