Move versioned generators into their own package

pkg/kubectl has a lot of files. Move everything generator related
into pkg/kubectl/generate (generic) or pkg/kubectl/generate/versioned
(type specific).

Move the DescriberFn and GeneratorFn out of kubectl/cmd/util and into
the respective versioned packages, along with tests.

pkg/kubectl/generate/versioned/serviceaccount_test.go

@@ -0,0 +1,63 @@
+/*
+Copyright 2016 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 versioned
+
+import (
+	"reflect"
+	"testing"
+
+	"k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+func TestServiceAccountGenerate(t *testing.T) {
+	tests := []struct {
+		name      string
+		expected  *v1.ServiceAccount
+		expectErr bool
+	}{
+		{
+			name: "foo",
+			expected: &v1.ServiceAccount{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: "foo",
+				},
+			},
+			expectErr: false,
+		},
+		{
+			expectErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			generator := ServiceAccountGeneratorV1{
+				Name: tt.name,
+			}
+			obj, err := generator.StructuredGenerate()
+			if !tt.expectErr && err != nil {
+				t.Errorf("unexpected error: %v", err)
+			}
+			if tt.expectErr && err != nil {
+				return
+			}
+			if !reflect.DeepEqual(obj.(*v1.ServiceAccount), tt.expected) {
+				t.Errorf("\nexpected:\n%#v\nsaw:\n%#v", tt.expected, obj.(*v1.ServiceAccount))
+			}
+		})
+	}
+}