Code review comment for lp://staging/~gz/launchpadlib/trivial_homeless_launchpadlib_dir

Leonard no longer works for Canonical.

I've confirmed the exiting tests pass with this branch merged (it would be nice if they were easier to run), and that the change fixes the bug reported. Given the state of the launchpadlib test suite, I don't see the point of blocking a trivial change like this indefinitely. It would be possible to add a unit test that confirms this specific behaviour change functions correctly, but by design it depends posixpath.expanduser and ntpath.expanduser behaviour. The former uses getuid and the pwd module to get the correct directory when HOME doesn't exist, which make setting up a sensible test environment onerous. I could fake out the os module to test the ValueError is raised correctly, but really Python's coverage of the os.path module should be sufficient.