Implement Docker healthcheck script in Go (#7105)

Go script makes it easy to read/maintain. Also updated the timeout
in Dockerfiles from 5s to default 30s and test interval to 1m

Higher timeout makes sense as server may sometimes respond slowly
if under high load as reported in #6974

Fixes #6974

Dockerfile.release

@@ -1,8 +1,22 @@
+FROM golang:1.11.4-alpine3.7
+
+ENV GOPATH /go
+ENV CGO_ENABLED 0
+
+WORKDIR /go/src/github.com/minio/
+
+RUN  \
+     apk add --no-cache git && \
+     go get -v -d github.com/minio/minio && \
+     cd /go/src/github.com/minio/minio/dockerscripts && \
+     go build -ldflags "-s -w" -o /usr/bin/healthcheck healthcheck.go
+
 FROM alpine:3.7
 
 LABEL maintainer="Minio Inc <dev@minio.io>"
 
-COPY dockerscripts/docker-entrypoint.sh dockerscripts/healthcheck.sh /usr/bin/
+COPY --from=0 /usr/bin/healthcheck /usr/bin/healthcheck
+COPY dockerscripts/docker-entrypoint.sh /usr/bin/
 
 ENV MINIO_UPDATE off
 ENV MINIO_ACCESS_KEY_FILE=access_key \
@@ -14,7 +28,7 @@ RUN \
      curl https://dl.minio.io/server/minio/release/linux-amd64/minio > /usr/bin/minio && \
      chmod +x /usr/bin/minio  && \
      chmod +x /usr/bin/docker-entrypoint.sh && \
-     chmod +x /usr/bin/healthcheck.sh
+     chmod +x /usr/bin/healthcheck
 
 EXPOSE 9000
 
@@ -22,7 +36,6 @@ ENTRYPOINT ["/usr/bin/docker-entrypoint.sh"]
 
 VOLUME ["/data"]
 
-HEALTHCHECK --interval=30s --timeout=5s \
-    CMD /usr/bin/healthcheck.sh
+HEALTHCHECK --interval=1m CMD healthcheck
 
 CMD ["minio"]