Adapt default image name and cache behavior

image.mk

@@ -2,7 +2,7 @@ OS := fedora
 
 IMAGE_PREFIX := ${DOCKER_IMAGE_PREFIX}
 ifeq ($(IMAGE_PREFIX),)
-IMAGE_PREFIX := icinga/
+IMAGE_PREFIX := icinga/$(OS)/
 endif
 
 REGISTRY := ${DOCKER_REGISTRY}
@@ -11,16 +11,19 @@ IMAGE_PREFIX := $(REGISTRY)/$(IMAGE_PREFIX)
 endif
 
 FROM := $(shell grep FROM Dockerfile | cut -d" " -f2)
+ifeq ($(VERSION),)
 VERSION := $(shell basename `pwd`)
-IMAGE := $(IMAGE_PREFIX)$(OS)-$(VERSION)$(IMAGE_SUFFIX)
+endif
+IMAGE := $(IMAGE_PREFIX)$(VERSION):$(VARIANT)
 
 all: pull build
 
 pull:
+	docker pull "$(IMAGE)" || true
 	docker pull "$(FROM)"
 
 build:
-	docker build -t "$(IMAGE)" .
+	docker build --cache-from "$(IMAGE)" --tag "$(IMAGE)" .
 
 push:
 	docker push "$(IMAGE)"