CIBT find the LAVA lab before calling releng

CIBT find the LAVA lab before calling releng

Add some logic to lava-labs-prepare:
- Search for the machine in the list of labs
- export the lab name if found

Call releng with the corresponding lab name in run-test-short

Send the job directly to the corresponding lab in lava-jobs-submit.
Keep the 'checking for device' in this script as well, just to make sure
the device is still available and can run the job. Otherwise the script
could be blocked there if the device status changes.

Change-Id: I50646b7fdb607cb9245a1d31e644eee45a2a2356
Signed-off-by: Loys Ollivier <lollivier@baylibre.com>