twister: prep for device testing

Add option to prepare for device testing by only building and storing
the needed data that can then later be executed and run on DUT using
--test-only.

This adds --prep-artifacts-for-testing which is the same as --build-only
and --device-testing and other options that were needed to make this
operational and produce the right binaries and files.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>