Fix access to libtpu

The jenkins SA did not have access to pull the libtpu docker image needed for the TPU VM build.
I started a TPU VM with that SA to grant it access, and added docker login setup to use authenticated docker commands.

Jenkinsfile

@@ -58,7 +58,7 @@ pipeline {
  }
  stage('tensorflow TPU') {
  options {
- timeout(time: 360, unit: 'MINUTES')
+ timeout(time: 240, unit: 'MINUTES')
  }
  steps {
  sh '''#!/bin/bash
@@ -177,6 +177,14 @@ pipeline {
  sh '''#!/bin/bash
  set -exo pipefail
 
+ # Login to docker to get access to gcr.io/cloud-tpu-v2-images/libtpu
+ # SA: [email protected]
+ # To grant access to a SA, start a TPU VM with that SA once.
+ METADATA=http:https://metadata.google.internal/computeMetadata/v1
+ SVC_ACCT=$METADATA/instance/service-accounts/default
+ ACCESS_TOKEN=$(/usr/bin/curl -s -H 'Metadata-Flavor: Google' $SVC_ACCT/token | cut -d'"' -f 4)
+ docker login --username oauth2accesstoken --password $ACCESS_TOKEN https://gcr.io
+
  ./tpu/build | ts
  ./push --tpu ${PRETEST_TAG}
  '''