Add better error reporting if a json spec can not be parsed

src/test/java/org/elasticsearch/test/rest/spec/RestSpec.java

@@ -71,9 +71,13 @@ public class RestSpec {
         RestSpec restSpec = new RestSpec();
         for (String path : paths) {
             for (File jsonFile : FileUtils.findJsonSpec(optionalPathPrefix, path)) {
+                try {
                     XContentParser parser = JsonXContent.jsonXContent.createParser(new FileInputStream(jsonFile));
                     RestApi restApi = new RestApiParser().parse(parser);
                     restSpec.addApi(restApi);
+                } catch (IOException ex) {
+                    throw new IOException("Can't parse rest spec file: [" + jsonFile + "]", ex);
+                }
             }
         }
         return restSpec;