Some cleanups.

* bzrlib/tests/test_server.py:
(ThreadWithException): Use a better name for the internal event.

* bzrlib/tests/test_http.py:
(RecordingServer.start_server): Use ThreadWithException.
(RecordingServer._accept_read_and_reply): Timeout is evil, don't
use it :)

* bzrlib/tests/http_server.py:
(TestingHTTPServerMixin.shutdown_client_socket): Don't pollute
ourput with caught exceptions.
(HttpServer.start_server): Not a daemonic thread anymore.