Dockerfile: Create dockerfile for 1.4 release branch (#3321)

Dockerfile

+FROM alpine:3.3
+
+ADD . /go-ethereum
+RUN \
+  apk add --update git go make gcc musl-dev         && \
+  (cd go-ethereum && make geth)                     && \
+  cp go-ethereum/build/bin/geth /geth               && \
+  apk del git go make gcc musl-dev                  && \
+  rm -rf /go-ethereum && rm -rf /var/cache/apk/*
+
+EXPOSE 8545
+EXPOSE 30303
+
+ENTRYPOINT ["/geth"]