Code review comment for lp:~lifeless/bzr/test-speed

This branch:
* Use copy, not deepcopy, to clone tests in test parameterisation.
* Make tests for finish_bzr_subprocess that really only care about the
   interface use StubProcess.
* Remove duplicated test_start_and_stop_working_dir test.
* Remove unnecessary use of an SFTP server connection to test the
   behaviour of TestCase.make_branch_and_tree.
* Refactor test_suite to make stubbing out the list of tests to load
possible without sacrificing coverage.

-Rob