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/ota_from_target_files
add ability to remove device assertions

do this by setting adding "TARGET_OTA_ASSERT_SKIP := true" in BoardConfig.mk

Change-Id: Ia832748ddc00320e0193d93be0883f4cc9208a35

Conflicts:
	core/Makefile
	tools/releasetools/ota_from_target_files

Conflicts:

	core/Makefile
	tools/releasetools/ota_from_target_files

Conflicts:

	tools/releasetools/ota_from_target_files