Add yamllint tox environment

Adds yamllint tox environment with bootstrapping non-voting
configuration. To work around a situation that some of overrides
contain entries for replacement and are not actually valid yamls,
all directories are copied to temporary directory, */values*
files are modified to be readable by yamllint.

Change-Id: I0084b243c1df1692178c59fb5b1b2fb7a4cbac44

tox.ini

@@ -20,3 +20,14 @@ commands =
   docstheme-build-translated.sh
 whitelist_externals =
   rm
+
+[testenv:lint]
+deps = yamllint
+commands =
+  bash -c "rm -rf {toxinidir}/.yamllint"
+  bash -c "mkdir -p {toxinidir}/.yamllint"
+  bash -c "cp -r $(ls {toxinidir}) {toxinidir}/.yamllint/"
+  bash -c "find {toxinidir}/.yamllint -type f -exec sed -i 's/%%%.*/XXX/g' \{\} +"
+  bash -c "yamllint -c {toxinidir}/yamllint.conf {toxinidir}/.yamllint/*/values*"
+whitelist_externals =
+  bash

yamllint.conf

@@ -0,0 +1,49 @@
+---
+
+yaml-files:
+- '*.yaml'
+- '*.yml'
+- '.yamllint'
+
+rules:
+  braces:
+    level: warning
+  brackets:
+    level: warning
+  colons:
+    level: warning
+  commas:
+    level: warning
+  comments:
+    level: warning
+  comments-indentation:
+    level: warning
+  document-end:
+    level: warning
+  document-start:
+    level: warning
+  empty-lines:
+    level: warning
+  empty-values:
+    level: warning
+  hyphens:
+    level: warning
+  indentation:
+    spaces: 2
+    indent-sequences: whatever
+    level: warning
+  key-duplicates:
+    level: warning
+  key-ordering: disable
+  line-length: disable
+  new-line-at-end-of-file:
+    level: warning
+  new-lines:
+    level: warning
+  octal-values:
+    level: warning
+  quoted-strings: disable
+  trailing-spaces: enable
+  truthy:
+    level: warning
+...