Add YAML sanity check

Adds a "validate" tox env for basic sanity checking of templates.
Currently it just validates that all of the .yaml files are in fact
valid YAML.  In the future we might want to add more, but this
seemed like a reasonable start.

Change-Id: I8091bbad0003b150e23dae5de4f465053c982229

tools/yaml-validate.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+#    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.
+
+import os
+import sys
+import traceback
+import yaml
+
+base_path = sys.argv[1]
+exit_val = 0
+failed_files = []
+
+def validate(filename):
+    try:
+        yaml.load(open(filename).read())
+    except Exception:
+        print(traceback.format_exc())
+        return 1
+    return 0
+
+for subdir, dirs, files in os.walk(base_path):
+    for f in files:
+        if f.endswith('.yaml'):
+            file_path = os.path.join(subdir, f)
+            failed = validate(file_path)
+            if failed:
+                failed_files.append(file_path)
+            exit_val |= failed
+
+if failed_files:
+    print('Validation failed on:')
+    for f in failed_files:
+        print(f)
+else:
+    print('Validation successful!')
+sys.exit(exit_val)

tox.ini

@@ -9,3 +9,6 @@ deps = -r{toxinidir}/requirements.txt
 
 [testenv:venv]
 commands = {posargs}
+
+[testenv:validate]
+commands = python ./tools/yaml-validate.py .