**Do you want to request a *feature* or report a *bug*?**

bug

**What is the current behavior?**

componentWillUnmount for inner instances is never called.

Here are 2 (jest) tests, the first works, not the second.

```js
import React from "react";
import renderer from "react-test-renderer";

test("top level componentWillUnmount works", () => {
  let count = 0;
  class A extends React.Component {
    componentWillUnmount() {
      count ++;
    }
    render() {
      return <div />;
    }
  }
  const inst = renderer.create(<A />);
  inst.unmount();
  expect(count).toEqual(1);
});

test("inner componentWillUnmount works", () => {
  let count = 0;
  class A extends React.Component {
    componentWillUnmount() {
      count ++;
    }
    render() {
      return <div />;
    }
  }
  const inst = renderer.create(
    <div>
      <A />
    </div>
  );
  inst.unmount();
  expect(count).toEqual(1);
});
```

**What is the expected behavior?**

The two test above should pass. All component that are unmounted should have the proper lifecycle, whatever the nesting is.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

React 15.4.0
transaction: ReactTestReconcileTransaction,
    nativeParent: null | ReactTestComponent,
    hostContainerInfo: Object,
    context: Object,
  ) {
    var element = this._currentElement;
    this._hostContainerInfo = hostContainerInfo;
    
    this.mountChildren(element.props.children, transaction, context);
  }
  receiveComponent(
    nextElement: ReactElement,
    transaction: ReactTestReconcileTransaction,
    context: Object,
  ) {
    this._currentElement = nextElement;
    
    this.updateChildren(nextElement.props.children, transaction, context);
  }
  getPublicInstance(): Object {
    var element = this._currentElement;
    var hostContainerInfo = this._hostContainerInfo;
    invariant(
      hostContainerInfo,
      'hostContainerInfo should be populated before ' +
      'getPublicInstance is called.'
    );
    return hostContainerInfo.createNodeMock(element);
  }
  toJSON(): ReactTestRendererJSON {