Adjust setup and teardown of route tests.

Closes #3856
* No longer call clearData and initData in test setup because
  migration.init is run during Ghost startup.  The unhandled
  error was a result of clearData removing all the tables while
  Ghost was running--there was a timing issue with the oauth middleware
  checking the refreshtokens table when it had just been deleted.

* Change teardown to first stop Ghost and then call clearData.