Choose architecture for building docker image

Signed-off-by: Alice Frosi <afrosi@de.ibm.com>

Makefile

@@ -16,6 +16,7 @@ LDFLAGS   := -w -s
 GOFLAGS   :=
 BINDIR    := $(CURDIR)/bin
 BINARIES  := helm tiller
+GO_ARCH   := amd64
 
 # Required for globs to work correctly
 SHELL=/bin/bash
@@ -60,8 +61,8 @@ check-docker:
 docker-binary: BINDIR = ./rootfs
 docker-binary: GOFLAGS += -a -installsuffix cgo
 docker-binary:
-	GOOS=linux GOARCH=amd64 CGO_ENABLED=0 $(GO) build -o $(BINDIR)/helm $(GOFLAGS) -tags '$(TAGS)' -ldflags '$(LDFLAGS)' k8s.io/helm/cmd/helm
-	GOOS=linux GOARCH=amd64 CGO_ENABLED=0 $(GO) build -o $(BINDIR)/tiller $(GOFLAGS) -tags '$(TAGS)' -ldflags '$(LDFLAGS)' k8s.io/helm/cmd/tiller
+	GOOS=linux GOARCH=$(GO_ARCH) CGO_ENABLED=0 $(GO) build -o $(BINDIR)/helm $(GOFLAGS) -tags '$(TAGS)' -ldflags '$(LDFLAGS)' k8s.io/helm/cmd/helm
+	GOOS=linux GOARCH=$(GO_ARCH) CGO_ENABLED=0 $(GO) build -o $(BINDIR)/tiller $(GOFLAGS) -tags '$(TAGS)' -ldflags '$(LDFLAGS)' k8s.io/helm/cmd/tiller
 
 .PHONY: docker-build
 docker-build: check-docker docker-binary
@@ -72,7 +73,7 @@ docker-build: check-docker docker-binary
 docker-binary-rudder: BINDIR = ./rootfs
 docker-binary-rudder: GOFLAGS += -a -installsuffix cgo
 docker-binary-rudder:
-	GOOS=linux GOARCH=amd64 CGO_ENABLED=0 $(GO) build -o $(BINDIR)/rudder $(GOFLAGS) -tags '$(TAGS)' -ldflags '$(LDFLAGS)' k8s.io/helm/cmd/rudder
+	GOOS=linux GOARCH=$(GO_ARCH) CGO_ENABLED=0 $(GO) build -o $(BINDIR)/rudder $(GOFLAGS) -tags '$(TAGS)' -ldflags '$(LDFLAGS)' k8s.io/helm/cmd/rudder
 
 .PHONY: docker-build-experimental
 docker-build-experimental: check-docker docker-binary docker-binary-rudder