Add new multi-stage Dockerfile for build

Dockerfile

@@ -1,10 +1,22 @@
-FROM python:3.6-alpine
+FROM golang:1.8.1-alpine as builder
 
-RUN pip install prometheus_client requests
+WORKDIR /go/src/github.com/infinityworksltd/docker-hub-exporter/
 
-ENV BIND_PORT 9170
+COPY ./ /go/src/github.com/infinityworksltd/docker-hub-exporter/
 
-ADD . /usr/src/app
-WORKDIR /usr/src/app
+RUN apk --update add ca-certificates \
+    && apk --update add --virtual build-deps git
 
-CMD ["python", "hub_exporter.py"]
+RUN go get \
+ && go test ./... \
+ && GOOS=linux go build -o app .
+
+FROM alpine
+
+RUN addgroup exporter \
+     && adduser -S -G exporter exporter \
+     && apk --update --no-cache add ca-certificates
+
+COPY --from=builder /go/src/github.com/infinityworksltd/docker-hub-exporter/app .
+
+ENTRYPOINT ["/app"]