Tidying up AlertDialog CTS tests

* Switch to Mockito for mocking listeners and querying calls.
* Much more targeted checks on how many times a listener has been
called in the specific scenario and with which parameter(s).
* Small cleanups in the code.

Change-Id: Ieb4e3bef2d49c19b2a029730d4e6a3aba405f04b
3 files changed