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

Conflicts:
	core/Makefile
	tools/buildinfo.sh
	tools/releasetools/ota_from_target_files

PS2: fix whitespaces

Change-Id: I300171045dff9e601b66854649eeb3a8cfa9cb5f