Tests should not depend on the state left by the previous test run.

This was achieved by:

* use a different preference in each method to reset the state of preferences configuration.
* clear cache after setting preferences, so that the new preference setting is used
* change password after setting the max preferred password lifetime duration, otherwise password event are not created and password is not detected as expired.
* rename test methods not to include number, we should not force test ordering, since we want tests to be independant.
* Also add one case of password actually expired