testing: prevent google-auto-auth from trying to read non-existent key file
testing: prevent google-auto-auth from trying to read non-existent key file

googleapis/google-cloud-node,jgeewax/gcloud-node,callmehiphop/gcloud-node,callmehiphop/gcloud-node,ofrobots/google-cloud-node,GoogleCloudPlatform/gcloud-node,ofrobots/google-cloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,jcking/google-cloud-node,GoogleCloudPlatform/gcloud-node,jcking/google-cloud-node,jcking/google-cloud-node,GoogleCloudPlatform/gcloud-node,googleapis/google-cloud-node,jgeewax/gcloud-node,ofrobots/google-cloud-node