add fetching into discovery client for OpenAPI v3

reflect latest struct changes

use correct discovery openapi test data layout

make the OpenAPIv3 interface less blue

field grouping

add copyrights

implement cached discovery client

add cached discovery tests

address review feedback

Kubernetes-commit: 075866b3e3ea029c243d82d8d6eb99e96d9c49d3

openapi/cached/groupversion.go

@@ -0,0 +1,45 @@
+/*
+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 cached
+
+import (
+	"sync"
+
+	openapi_v3 "github.com/google/gnostic/openapiv3"
+	"k8s.io/client-go/openapi"
+)
+
+type groupversion struct {
+	delegate openapi.GroupVersion
+	once     sync.Once
+	doc      *openapi_v3.Document
+	err      error
+}
+
+func newGroupVersion(delegate openapi.GroupVersion) *groupversion {
+	return &groupversion{
+		delegate: delegate,
+	}
+}
+
+func (g *groupversion) Schema() (*openapi_v3.Document, error) {
+	g.once.Do(func() {
+		g.doc, g.err = g.delegate.Schema()
+	})
+
+	return g.doc, g.err
+}