twister: run as device, even if simulation is supported

Some hardware boards are supported in qemu as simulation platforms. If
we are testing with the real hardware, make sure we treat this as a
device and not as a simulator. First priority when initializing a
handler is to check if device testing is requested, then we can handle
the rest without --device-testing.

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