Build docker image of nomulus tool (#142)

* Build docker image of nomulus tool

In the course of "gradle build", build a docker image of nomulus tool so that
users can run this to allow us to bundle the java version with the image.

release/cloudbuild-nomulus.yaml

@@ -22,9 +22,27 @@ steps:
 # Run tests
 - name: 'gcr.io/${PROJECT_ID}/builder:latest'
   args: ['./gradlew', 'test', '-PskipDockerIncompatibleTests=true']
-# Build the tool binary.
+# Build the tool binary and image.
 - name: 'gcr.io/${PROJECT_ID}/builder:latest'
   args: ['release/build_nomulus_for_env.sh', 'tool', 'output']
+# Tag the tool image and push it to the registry.
+- name: 'gcr.io/${PROJECT_ID}/builder:latest'
+  entrypoint: /bin/bash
+  args:
+    - -c
+    - |
+      docker tag nomulus-tool gcr.io/${PROJECT_ID}/nomulus-tool:${TAG_NAME}
+      docker push gcr.io/${PROJECT_ID}/nomulus-tool:${TAG_NAME}
+# Get the tool image digest and substitute in the digest in the tagging yaml file.
+- name: 'gcr.io/${PROJECT_ID}/builder:latest'
+  entrypoint: /bin/bash
+  args:
+  - -c
+  - |
+    digest=$(gcloud container images list-tags gcr.io/${PROJECT_ID}/nomulus-tool \
+      --format="get(digest)" --filter="tags = ${TAG_NAME}")
+    sed -i s/'$${_IMAGE}'/nomulus-tool/g release/cloudbuild-tag.yaml
+    sed -i s/':$${TAG_NAME}'/@$digest/g release/cloudbuild-tag.yaml
 # Build and package the deployment files for alpha.
 - name: 'gcr.io/${PROJECT_ID}/builder:latest'
   args: ['release/build_nomulus_for_env.sh', 'alpha', 'output']
@@ -44,6 +62,7 @@ artifacts:
     paths:
     - 'output/*.tar'
     - 'output/nomulus.jar'
+    - 'release/cloudbuild-tag.yaml'
     - 'release/cloudbuild-sync.yaml'
     - 'release/cloudbuild-beam.yaml'
 timeout: 3600s