Horizon angular mocks

Summary:

Create shared client-side mock objects in angular to ensure high quality client-side tests.

Motivation:

Currently random mock objects are created inside of spec files to make writing unit tests easier. This approach has some drawback though:

* mocks are not sharable between specs.
* mocks are usually too simple.
* mocks may not be consistent between spec files.
* mocks are not tested themselves.
* hard to maintain and manage.

Description:

* mocks should reside in `.mock.js` files and be loaded only in test runner page
* mocks should be loaded after production code files, before spec code files.
* mocks should be sharable between specs.
* mocks are not belong to specs, they should have a 1:1 relationship with the object it try to mock.
* mocks should be at a level as low as possible, maybe where JavaScript cannot reach directly.
* mocks must be tested theme self.
* mocks should be easy to find, use and manage.

Scope:

This BP will provides these mocks:
* mockWindow
* mockOpenStackHttpServer

UX:
N/A

Outside Dependencies:
N/A

Doc Impact:
May need to update the Angular part.