Revert "twister: Update path structure for tests"

This reverts commit 21eb27c5.

This change has been a source of much trouble and ends up preventing us
from tracking test results across tree. It uses the repo name as the
namespace, and that is not always the same and does not have to be
called 'zephyr', depending on where you are running and in which
environment.

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