Test against https.

* bzrlib/tests/test_http.py:
(load_tests): Get rid of TestAdapter daughter classes, they are
useless. Add parametrization against http/https for activity
tests.
(ActivityServerMixin, ActivityHTTPServer, ActivityHTTPSServer):
Make HTTP[S] servers.
(PreRecordedRequestHandler.handle_one_request): Be defensive
against threads being non-deterministic.
(TestActivity.test_http_get): Use parametrized test server.

* bzrlib/tests/https_server.py:
(HTTPSServer.__init__): Add protocol_version parameter for tests
purposes.