Image Promoter: Allows images to be pushed immediately after being built

In the current version, due to how make works, when building all the conformance
images (make all-push WHAT=all-conformance), ALL the images are being built first
before being pushed.

This PR will allow images to be built and pushed immediately afterwards, so the first
images that have been succesfully built are already pushed and promotable, even if
the the task failed on the last image, or it timed out.

test/images/Makefile

@@ -37,4 +37,7 @@ all-container:
 all-push: all-container
 	./image-util.sh push $(WHAT)
 
-.PHONY: all all-push all-container
+all-build-and-push:
+	./image-util.sh build_and_push ${WHAT}
+
+.PHONY: all all-build-and-push all-push all-container

test/images/cloudbuild.yaml

@@ -19,7 +19,7 @@ steps:
     - REGISTRY=gcr.io/k8s-staging-e2e-test-images
     # TODO(claudiub): Readd the REMOTE_DOCKER_URL_${os_version} to reenable the Windows test image building process.
     args:
-    - all-push
+    - all-build-and-push
 substitutions:
   # _GIT_TAG will be filled with a git-based tag for the image, of the form vYYYYMMDD-hash, and
   # can be used as a substitution

test/images/image-util.sh

@@ -237,6 +237,14 @@ push() {
   docker manifest push --purge "${REGISTRY}/${image}:${TAG}"
 }
 
+# This function is for building AND pushing images. Useful if ${WHAT} is "all-conformance".
+# This will allow images to be pushed immediately after they've been pushed.
+build_and_push() {
+  image=$1
+  build "${image}"
+  push "${image}"
+}
+
 # This function is for building the go code
 bin() {
   local arch_prefix=""