Closes AdoptOpenJDK/openjdk-docker/issues#119 - Add hadolint for lint…

…ing Dockerfiles

.travis.yml

@@ -1,6 +1,4 @@
 language: sh
-install:
-- sudo apt-get update && sudo apt-get install --yes docker
 
 script:
-- ./build_all.sh
+- ./linter.sh

README.md

@@ -60,6 +60,8 @@ The Dockerfiles and associated scripts found in this project are licensed under
 
 # We should now have the proper manifest lists pushed to hub.docker.com to support multi-arch pulls.
 ```
+## Linting dockerfiles (via [hadolint](https://github.com/hadolint/hadolint))
+To lint generated dockerfiles run [./linter.sh](./linter.sh) - script will download hadolint binary and check all dockerfiles.
 
 # Info on other scripts
 ```

linter.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+
+################################################################################
+# 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
+#
+#      https://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.
+################################################################################
+
+################################################################################
+#
+# This script downloads and executes hadolint. It will be run automatically
+# by Travis on every push. You can run it manually to validate your changes.
+#
+################################################################################
+
+set -eu
+
+hadolintDir="hadolint"
+hadolintCmd="${hadolintDir}/hadolint"
+
+install()
+{
+  mkdir -p "${hadolintDir}"
+
+  wget -O ${hadolintDir}/hadolint "https://github.com/hadolint/hadolint/releases/download/v1.16.0/hadolint-Linux-x86_64"
+  chmod +x "${hadolintCmd}"
+  "${hadolintCmd}" --version
+}
+
+check()
+{
+    find . -name "Dockerfile*" -exec sh -c "./${hadolintCmd}  {};echo " \;
+}
+
+if [[ ! -d "${hadolintDir}" ]] ; then
+  install
+fi
+check