Merge branch 'docker-cache' into 'master'

Don't cache Docker layers

See merge request !6

image.mk

@@ -22,11 +22,10 @@ endif
 all: pull build
 
 pull:
-	docker pull "$(IMAGE):$(VARIANT)" || true
 	docker pull "$(FROM)"
 
 build:
-	docker build --cache-from "$(IMAGE):$(VARIANT)" --tag "$(IMAGE):$(VARIANT)" .
+	docker build --tag "$(IMAGE):$(VARIANT)" .
 ifdef IMAGE_EXTRA_TAG
 	docker tag "$(IMAGE):$(VARIANT)" "$(IMAGE):$(IMAGE_EXTRA_TAG)"
 endif