Add docker release files. (#4473)

We used to release by building directly on the docker
hub auto build process, which is sufficient for edge
but it is not a good idea to do it for stable releases.

Do not build docker release binaries again, but instead
use the released binaries themselves which are signed
and validated.

Dockerfile

@@ -11,7 +11,7 @@ WORKDIR /go/src/github.com/minio/
 RUN  \
      apk add --no-cache ca-certificates && \
      apk add --no-cache --virtual .build-deps git go musl-dev && \
-     echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \     
+     echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \
      go get -v -d github.com/minio/minio && \
      cd /go/src/github.com/minio/minio && \
      go install -v -ldflags "$(go run buildscripts/gen-ldflags.go)" && \