Added HEALTHCHECK in release Dockerfiles (#4550)

A new script `healthcheck.sh` checks for http status 200/404

buildscripts/healthcheck.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+#
+# Minio Cloud Storage, (C) 2017 Minio, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+_init () {
+    address="http://127.0.0.1:9000"
+    resource="/minio/index.html"
+}
+
+HealthCheckMain () {
+    # Get the http response code
+    http_response=$(curl -s -o /dev/null -I -w "%{http_code}" ${address}${resource})
+
+    # If http_repsonse is 200 - server is up. 
+    # When MINIO_BROWSER is set to off, curl responds with 404. We assume that the the server is up
+    [ "$http_response" == "200" ] || [ "$http_response" == "404" ]
+}
+
+_init && HealthCheckMain