Switch cloudbuild image to gcr.io/cloud-builders/docker (#2154)

Author: mdbooth

cloudbuild.yaml

@@ -9,21 +9,19 @@ options:
   substitution_option: ALLOW_LOOSE
   machineType: 'N1_HIGHCPU_8'
 steps:
-  - name: gcr.io/k8s-testimages/gcb-docker-gcloud
+  - name: gcr.io/cloud-builders/docker
     entrypoint: bash
-    env:
-    # Required because the default HOME is /builder/root but buildx is
-    # installed in /root/.docker. Not setting this results in docker not
-    # finding buildx during make.
-    - HOME=/root
     args:
     - -c
     - |
       set -xeuo pipefail
 
-      # Run the image's buildx entrypoint to initialise the build environment
-      # appropriately for the image before running make
-      /buildx-entrypoint version
+      # Initialise a new builder instance
+      docker buildx create --use
+
+      # Create docker credentials for pushing to gcr.io from our inherited
+      # gcloud credentials
+      gcloud auth configure-docker
 
       make push-multiarch-images \
         REGISTRY=gcr.io/$PROJECT_ID \