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