Add verbose mode to boilerplate

hack/verify-boilerplate.sh -v will now print out why the file does
not match along with a diff if possible.

Note: boilerplate.py now has a unit test that is run along with
hack/verify-boilerplate.sh.

hack/boilerplate/test/pass.go

@@ -0,0 +1,17 @@
+/*
+Copyright 2014 The Kubernetes Authors.
+
+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.
+*/
+
+package main