Add a helper tool to emit Makefile snippets

This loads the whole go universe one time, so should be faster that
repeated calls to `go list`

hack/make-rules/helpers/go2make/testdata/dir-with-gofiles/foo.go

@@ -0,0 +1,20 @@
+/*
+Copyright 2017 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 gofiles
+
+func foo() {
+}