Add more tests for OC\Core\Controller\LostController

- remove testResetFormUnsuccessful as it is now splitted up in different test cases
- add testResetFormInvalidToken to check if timestamp and token are present
- add testResetFormInvalidTokenMatch to check if the saved token matches the provided
- add testResetFormExpiredToken to check if expiration detection works
- add testResetFormValidToken to check if detection of valid tokens works