rethrow instead of throwing new Error (#1831)
rethrow instead of throwing new Error (#1831)

Rethrow perserves the stack trace.
GoogleCloudPlatform/gcloud-node,jcking/google-cloud-node,GoogleCloudPlatform/gcloud-node,jcking/google-cloud-node,GoogleCloudPlatform/gcloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,googleapis/google-cloud-node,ofrobots/google-cloud-node,jgeewax/gcloud-node,callmehiphop/gcloud-node,jcking/google-cloud-node,googleapis/google-cloud-node,ofrobots/google-cloud-node,jgeewax/gcloud-node,callmehiphop/gcloud-node,ofrobots/google-cloud-node