Fix makefiles for NFS and Gluster images

contrib/for-tests/volumes-tester/gluster/Makefile

@@ -3,9 +3,11 @@ all: push
 TAG = 0.1
 
 container:
-	docker build -t gcr.io/google_containers/volume-gluster:$(TAG) .
+	docker build -t gcr.io/google_containers/volume-gluster . # Build new image and automatically tag it as latest
+	docker tag gcr.io/google_containers/volume-gluster gcr.io/google_containers/volume-gluster:$(TAG)  # Add the version tag to the latest image 
 
 push: container
-	gcloud preview docker push gcr.io/google_containers/volume-gluster:$(TAG)
+	gcloud preview docker push gcr.io/google_containers/volume-gluster # Push image tagged as latest to repository
+	gcloud preview docker push gcr.io/google_containers/volume-gluster:$(TAG) # Push version tagged image to repository (since this image is already pushed it will simply create or update version tag)
 
 clean:

contrib/for-tests/volumes-tester/nfs/Makefile

@@ -3,9 +3,11 @@ all: push
 TAG = 0.1
 
 container:
-	docker build -t gcr.io/google_containers/volume-nfs:$(TAG) .
+	docker build -t gcr.io/google_containers/volume-nfs . # Build new image and automatically tag it as latest
+	docker tag gcr.io/google_containers/volume-nfs gcr.io/google_containers/volume-nfs:$(TAG) # Add the version tag to the latest image 
 
 push: container
-	gcloud preview docker push gcr.io/google_containers/volume-nfs:$(TAG)
+	gcloud preview docker push gcr.io/google_containers/volume-nfs # Push image tagged as latest to repository
+	gcloud preview docker push gcr.io/google_containers/volume-nfs:$(TAG) # Push version tagged image to repository (since this image is already pushed it will simply create or update version tag)
 
 clean: