Allow the use of multiple Linaro toolchains

Enable building with a8 optimized version of Linaro
Thanks to christopher!
If not using custom toolchain use default toolchain folder

Change-Id: I7a35c2a318d17fe3013b056c08b9cb1347b7b329
More info during installation of a new ROM

Change-Id: I618511c3e0d47e931a02eec6429e871bd4b6b70a

Conflicts:

	tools/releasetools/ota_from_target_files