Add validate-json tox target

This is a simple JSON validation script based on demjson python library,
we do some shell script trickeries to exit properly if there is a
failure for tox (should probably patch demjson to properly exit
instead).

Change-Id: I930908336deef7daeaab5b55ba2031c64698d880
Implements: blueprint json-validation-gate

test-requirements.txt

@@ -0,0 +1 @@
+demjson

tools/validate-json.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+set -e
+
+TMPFILE=$(mktemp)
+ret=0
+
+function clean {
+    rm -f ${TMPFILE}
+}
+trap clean EXIT
+
+for f in $(find docker/ -type f -name '*.json');do
+    jsonlint -s ${f} >${TMPFILE}
+    egrep -q 'has errors$' ${TMPFILE} && { cat ${TMPFILE}; ret=1 ;}
+done
+
+cat ${TMPFILE}
+
+exit ${ret}

tox.ini

@@ -0,0 +1,11 @@
+[tox]
+skipsdist = True
+envlist = validate-json
+minversion = 1.6
+
+[testenv]
+deps = -r{toxinidir}/test-requirements.txt
+
+[testenv:validate-json]
+commands = 
+    {toxinidir}/tools/validate-json.sh