Improvements for debug mode

Return back `cd docker` part to be less invasive,
and add `-debug` postfix for image

Makefile

@@ -8,18 +8,9 @@ ifeq ($(RACE),1)
     CGO_ENABLED=1
 endif
 
-ifeq ($(DEBUG),1)
-	BUILD_FLAGS += -gcflags "-N -l"
-endif
-
 LOCAL_BUILD_FLAGS ?= $(BUILD_FLAGS)
 LDFLAGS ?= -X=main.version=$(VERSION)
-
-ifeq ($(DEBUG),1)
-	DOCKERFILE = docker/DebugDockerfile
-else
-	DOCKERFILE = docker/Dockerfile
-endif
+DOCKERDIR = docker
 
 IMAGE ?= registry.opensource.zalan.do/acid/$(BINARY)
 TAG ?= $(VERSION)
@@ -31,6 +22,14 @@ VERSION ?= $(shell git describe --tags --always --dirty)
 DIRS := cmd pkg
 PKG := `go list ./... | grep -v /vendor/`
 
+ifeq ($(DEBUG),1)
+	DOCKERFILE = DebugDockerfile
+	DEBUG_POSTFIX := -debug
+	BUILD_FLAGS += -gcflags "-N -l"
+else
+	DOCKERFILE = Dockerfile
+endif
+
 PATH := $(GOPATH)/bin:$(PATH)
 SHELL := env PATH=$(PATH) $(SHELL)
 
@@ -52,8 +51,8 @@ docker-context: scm-source.json linux
 	mkdir -p docker/build/
 	cp build/linux/${BINARY} scm-source.json docker/build/
 
-docker: ${DOCKERFILE} docker-context
-	docker build --rm -t "$(IMAGE):$(TAG)" -f "${DOCKERFILE}" .
+docker: ${DOCKERDIR}/${DOCKERFILE} docker-context
+	cd "${DOCKERDIR}" && docker build --rm -t "$(IMAGE):$(TAG)$(DEBUG_POSTFIX)" -f "${DOCKERFILE}" .
 
 indocker-race:
 	docker run --rm -v "${GOPATH}":"${GOPATH}" -e GOPATH="${GOPATH}" -e RACE=1 -w ${PWD} golang:1.8.1 bash -c "make linux"