Create multi-arch image

For linux arm64 and amd64, as per #586.

I moved the builder image into the same dockerfile, and bumped the Go
version on it. It didn't seem like the builder dockerfile worked with
the latest code anyway (the go modules require go 1.15 and higher).

This requires a recent enough docker install with buildx, as well as
an arm64 builder.

BASEIMAGE is changed to not specify an arch, so that the image will
build on its native arch in buildx.

Example image is on docker hub as:

    kelvie/node-problem-detector:v0.8.10-5-gb0fa610

Makefile

@@ -23,6 +23,7 @@ all: build
 
 # PLATFORMS is the set of OS_ARCH that NPD can build against.
 LINUX_PLATFORMS=linux_amd64 linux_arm64
+DOCKER_PLATFORMS=linux/amd64,linux/arm64
 PLATFORMS=$(LINUX_PLATFORMS) windows_amd64
 
 # VERSION is the version of the binary.
@@ -74,7 +75,7 @@ endif
 # The debian-base:v1.0.0 image built from kubernetes repository is based on
 # Debian Stretch. It includes systemd 232 with support for both +XZ and +LZ4
 # compression. +LZ4 is needed on some os distros such as COS.
-BASEIMAGE:=k8s.gcr.io/debian-base-amd64:v2.0.0
+BASEIMAGE:=k8s.gcr.io/debian-base:v2.0.0
 
 # Disable cgo by default to make the binary statically linked.
 CGO_ENABLED:=0
@@ -239,8 +240,8 @@ $(NPD_NAME_VERSION)-%.tar.gz: $(ALL_BINARIES) test/e2e-install.sh
 
 build-binaries: $(ALL_BINARIES)
 
-build-container: build-binaries Dockerfile
-	docker build -t $(IMAGE) --build-arg BASEIMAGE=$(BASEIMAGE) --build-arg LOGCOUNTER=$(LOGCOUNTER) .
+build-container: clean Dockerfile
+	docker buildx build --platform $(DOCKER_PLATFORMS) -t $(IMAGE) --build-arg BASEIMAGE=$(BASEIMAGE) --build-arg LOGCOUNTER=$(LOGCOUNTER) .
 
 $(TARBALL): ./bin/node-problem-detector ./bin/log-counter ./bin/health-checker ./test/bin/problem-maker
 	tar -zcvf $(TARBALL) bin/ config/ test/e2e-install.sh test/bin/problem-maker
@@ -252,7 +253,7 @@ build-tar: $(TARBALL) $(ALL_TARBALLS)
 build: build-container build-tar
 
 docker-builder:
-	docker build -t npd-builder ./builder
+	docker build -t npd-builder . --target=builder
 
 build-in-docker: clean docker-builder
 	docker run \
@@ -260,8 +261,12 @@ build-in-docker: clean docker-builder
 		-c 'cd /gopath/src/k8s.io/node-problem-detector/ && make build-binaries'
 
 push-container: build-container
+	# So we can push to docker hub by setting REGISTRY
+ifneq (,$(findstring gcr.io,$(REGISTRY)))
 	gcloud auth configure-docker
-	docker push $(IMAGE)
+endif
+	# Build should be cached from build-container
+	docker buildx build --push --platform $(DOCKER_PLATFORMS) -t $(IMAGE) --build-arg BASEIMAGE=$(BASEIMAGE) --build-arg LOGCOUNTER=$(LOGCOUNTER) .
 
 push-tar: build-tar
 	gsutil cp $(TARBALL) $(UPLOAD_PATH)/node-problem-detector/