Build multi-arch images

Change-Id: If4ba053b7cf5a704afcb3f7e4a19aeed8440f3d9

.zuul.yaml

@@ -6,6 +6,9 @@
       docker_images:
         - context: .
           repository: vexxhost/node-labeler
+          arch:
+            - linux/amd64
+            - linux/arm64
 
 - job:
     name: node-labeler:image:upload

Dockerfile

@@ -1,8 +1,10 @@
 FROM golang:1.13 AS builder
 WORKDIR /go/src/app
 COPY . .
-RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build
+RUN CGO_ENABLED=0 GOOS=linux go build
 
-FROM scratch
+# NOTE(mnaser): https://github.com/containers/skopeo/issues/991
+# FROM scratch
+FROM debian:stable-slim
 COPY --from=builder /go/src/app/node-labeler /node-labeler
 ENTRYPOINT ["/node-labeler"]