Reset services before every test

Reset services before every test

Trying to avoid resetting services introduces a lot of complexity and
several bugs. We were doing a reset for 70% of @group Database tests
anyway.

Instead:

* Reset services at the start of MediaWikiTestCase::run().
* Capture the actual original service container instead of making a
  special shared service container.
* The test-isolated local service container can now only be initialised
  non-statically. Revert the recent conversion of overrideMwServices()
  to static.
* Store a reference to the local service container in the test case
  object. In MediaWikiTestCase, always use the original or local service
  container directly, to avoid confusion about which one is active at
  the time.
* Remove a lot of unnecessary teardown
* Always call ServiceContainer::destroy() before forceGlobalInstance()
  since the memory is not otherwise freed.

Change-Id: I4a17c1c7ec92c14e3bc471f0216473ebe19477b9