Add the ability to run testimage against zephyr machines.
Unfortunately, this exposes a bug in meta-zephyr with TESTIMAGE_AUTO not
working correctly. So, work around this until it can be fixed upstream.
Also, qemu-cortex-a53 does not successfully pass any of the tests it
successfully builds. So, don't run testimage until that can be
addressed.
Signed-off-by: Jon Mason <jon.mason@arm.com>
Jon Mason