Allow specifying kernel toolchain and prefix

Change-Id: Ib75cfe772e073f2196455f3e3dfba247f6b3feff

Conflicts:
	core/tasks/kernel.mk
releasetools: Kill stray ] with fire

Change-Id: I9396af24533396ce0576774843de4886938cac94

Conflicts:
	tools/releasetools/ota_from_target_files
build: allow mounting by partition name through edify
With more devices migrating over to emulated storage there is a need for
increased flexibility when mounting partitions. Edify scripts currently lack
the ability to mount emmc partitions by their labels, so busybox is used
as a reliable alternative.

This allows partitions to be mounted by name while still maintaining
compatibility with older recoveries.

To use define TARGET_SETS_FSTAB in the device's make files

Change-Id: I905740dd566f451b7ac48579a85e1b39a8cfd31a