Quit browsers between tests

Before, pyfuct only quits browsers on end of testcase (`tearDownClass`).
This will avoid keep multiple browsers open, that aren't used.

In case property `reuse_browser` is configured to true, we mantain only
the default browser open and clear his session.
Please, create a method that takes off the browser from `self.browsers` and quits it, so that you don't have to recreate the list in L46.