Merge pull request #465 from mboersma/build-no-cache

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

Author: mboersma

.travis.yml

@@ -4,6 +4,7 @@ branches:
     - master
 env:
   DEV_REGISTRY=quay.io
+  DOCKER_BUILD_FLAGS="--pull --no-cache"
 services:
   - docker
 sudo: required

Makefile

@@ -46,7 +46,7 @@ test-cover:
 	${DEV_ENV_CMD} test-cover.sh
 
 docker-build: build
-	docker build --rm -t ${IMAGE} rootfs
+	docker build ${DOCKER_BUILD_FLAGS} -t ${IMAGE} rootfs
 	docker tag ${IMAGE} ${MUTABLE_IMAGE}
 
 check-kubectl: