Beginning of rewrite apply merge-logic using visitor pattern.

Major changes:
- Don't generate a patch, instead generate the merged object so it can be used with PUT
- Separate tree parsing logic to collate items in a list from the delete / merge / replace / add logic when merging
- Use openapi for merge strategy metadata so it works with extensions and version skew
- Support multi-field mergekeys when merging lists
- Support replace strategy for maps
- Reduce complexity of generating order when merging lists - keep the locally defined order and append remote only-items

Continue to support:
- Explicitly setting fields to null
- Merging lists of primitives
- Don't randomize ordering when merging lists

TODO:
- Retain keys
- Conflict detection

pkg/kubectl/apply/list_element.go

@@ -0,0 +1,82 @@
+/*
+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 apply
+
+// ListElement contains the recorded, local and remote values for a field
+// of type list
+type ListElement struct {
+	// FieldMetaImpl contains metadata about the field from openapi
+	FieldMetaImpl
+
+	// HasElementData contains whether the field was set
+	HasElementData
+
+	// ListElementData contains the value a field was set to
+	ListElementData
+
+	// Values contains the combined recorded-local-remote value of each item in the list
+	// Present for lists that can be merged only.  Contains the items
+	// from each of the 3 lists merged into single Elements using
+	// the merge-key.
+	Values []Element
+}
+
+// Merge implements Element.Merge
+func (e ListElement) Merge(v Strategy) (Result, error) {
+	return v.MergeList(e)
+}
+
+var _ Element = &ListElement{}
+
+// ListElementData contains the recorded, local and remote data for a list
+type ListElementData struct {
+	// recorded contains the value of the field from the recorded object
+	Recorded []interface{}
+
+	// Local contains the value of the field from the recorded object
+	Local []interface{}
+
+	// Remote contains the value of the field from the recorded object
+	Remote []interface{}
+}
+
+// GetRecorded implements Element.GetRecorded
+func (e ListElementData) GetRecorded() interface{} {
+	// https://golang.org/doc/faq#nil_error
+	if e.Recorded == nil {
+		return nil
+	}
+	return e.Recorded
+}
+
+// GetLocal implements Element.GetLocal
+func (e ListElementData) GetLocal() interface{} {
+	// https://golang.org/doc/faq#nil_error
+	if e.Local == nil {
+		return nil
+	}
+	return e.Local
+}
+
+// GetRemote implements Element.GetRemote
+func (e ListElementData) GetRemote() interface{} {
+	// https://golang.org/doc/faq#nil_error
+	if e.Remote == nil {
+		return nil
+	}
+	return e.Remote
+}