Add unit tests for SSH-backed repositories.

This adds some unit tests for testing connections to SSH-backed repositories
using rbssh. These tests are a bit special, and require access to some
arbitrary repositories which must be configured in settings.py. A template
for these have been provided in settings_local.py.tmpl. If these aren't
defined, the tests will just skip.

Ran the unit tests on Windows and Linux (with the other changes). They all pass.