feat(Makefile): set docker build flags via environment variable

Author: mboersma

.travis.yml

@@ -6,6 +6,8 @@ branches:
     - master
 services:
   - docker
+env:
+  - DOCKER_BUILD_FLAGS="--pull --no-cache"
 sudo: required
 script:
   - make bootstrap docker-build test

Makefile

@@ -28,7 +28,7 @@ build:
 	@echo Nothing to do.
 
 docker-build:
-	docker build --pull --rm -t ${IMAGE} rootfs
+	docker build ${DOCKER_BUILD_FLAGS} -t ${IMAGE} rootfs
 	docker tag ${IMAGE} ${MUTABLE_IMAGE}
 
 deploy: docker-build docker-push

versioning.mk

@@ -1,5 +1,6 @@
 MUTABLE_VERSION ?= canary
 VERSION ?= git-$(shell git rev-parse --short HEAD)
+DOCKER_BUILD_FLAGS ?= --pull
 
 IMAGE := ${DEIS_REGISTRY}${IMAGE_PREFIX}/${SHORT_NAME}:${VERSION}
 MUTABLE_IMAGE := ${DEIS_REGISTRY}${IMAGE_PREFIX}/${SHORT_NAME}:${MUTABLE_VERSION}