* bzrlib/transport/sftp.py: Move the test servers code to tests.stub_sftp. (get_test_permutations): Import the test servers only when the tests are run.
* bzrlib/tests/test_transport.py: (TestSSHConnections.test_bzr_connect_to_bzr_ssh): Get the tests servers from tests.stub_sftp.
* bzrlib/tests/test_sftp_transport.py: Get the tests servers from tests.stub_sftp.
* bzrlib/tests/stub_sftp.py: Fix imports, move the test servers code from transport.sftp.