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.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python
+
+# Copyright 2015 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.
+
+True