From review comments, use a private scheme for testing.
* bzrlib/transport/__init__.py: (_unregister_urlparse_netloc_protocol): New function.
* bzrlib/tests/transport_util.py: (InstrumentedTransport.__init__): Use a dedicated scheme. (TestCaseWithConnectionHookedTransport.setUp): Reworked to register the new transport. (TestCaseWithConnectionHookedTransport.get_url): Use our dedicated scheme. (TestCaseWithConnectionHookedTransport.install_hooks, TestCaseWithConnectionHookedTransport.reset_hooks): Registering transport is setUp job.