Mechanical: Move mock packages out of ./pkg

Mechanical execution of:

```
git mv ./pkg/mock/mockserver ./client/pkg/mock
git mv ./pkg/mock/{mockstorage,mockstore,mockwait} ./server/pkg/mock
```

The packages depend on etcd API / protos - so they are NOT etcd-dependencies.
In such situation thay should be placed in 'pkg' folder.

server/mock/mockwait/doc.go

@@ -0,0 +1,16 @@
+// Copyright 2016 The etcd 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 mockwait provides mock implementations for pkg/wait.
+package mockwait

server/mock/mockwait/wait_recorder.go

@@ -0,0 +1,47 @@
+// Copyright 2015 The etcd 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 mockwait
+
+import (
+	"go.etcd.io/etcd/v3/pkg/testutil"
+	"go.etcd.io/etcd/v3/pkg/wait"
+)
+
+type WaitRecorder struct {
+	wait.Wait
+	testutil.Recorder
+}
+
+type waitRecorder struct {
+	testutil.RecorderBuffered
+}
+
+func NewRecorder() *WaitRecorder {
+	wr := &waitRecorder{}
+	return &WaitRecorder{Wait: wr, Recorder: wr}
+}
+func NewNop() wait.Wait { return NewRecorder() }
+
+func (w *waitRecorder) Register(id uint64) <-chan interface{} {
+	w.Record(testutil.Action{Name: "Register"})
+	return nil
+}
+func (w *waitRecorder) Trigger(id uint64, x interface{}) {
+	w.Record(testutil.Action{Name: "Trigger"})
+}
+
+func (w *waitRecorder) IsRegistered(id uint64) bool {
+	panic("waitRecorder.IsRegistered() shouldn't be called")
+}