Allow override of device asserts, including multi-device support.

Set in board file with TARGET_OTA_ASSERT_DEVICE.
(cherry-picked from commit 0f452f21fc9323b9d1fe746161761cf40aaa5030)

Change-Id: I3d06bdc0e3e26bde0c0e646accd050364f9713b9

Conflicts:
	core/Makefile
	tools/releasetools/edify_generator.py
	tools/releasetools/ota_from_target_files

Conflicts:
	core/Makefile
	tools/releasetools/edify_generator.py
	tools/releasetools/ota_from_target_files
build:  Add USE_SET_METADATA tag

On some of the older devices the recovery doesn't support
metadata when setting permissions.  This allows to use
set_perm vs set_metadata you will need to set
USE_SET_METADATA := false inside your boardconfig.mk

Change-Id: Ib6cf97b5ca28cee8a87975231f3a61b156e77d29

Conflicts:
	core/Makefile