qa_crowbarsetup: Fix test image download
qa_crowbarsetup: Fix test image download

When calculating the urls for the testing iso on the controller node,
the TESTHEAD variable is needed to get the correct image.

vmoravec/automation,gosipyan/automation,gosipyan/automation,aspiers/automation,aspiers/automation,SUSE-Cloud/automation,SUSE-Cloud/automation,vmoravec/automation,aspiers/automation,aspiers/automation,SUSE-Cloud/automation,vmoravec/automation,gosipyan/automation,vmoravec/automation,SUSE-Cloud/automation,gosipyan/automation