Support a push strategy for custom buildout directories

[rfleschenberg]

It would be nice if I could supply a custom buildout directory as a local path on the ansible control machine.

• It would support a wider range of repository structures. Currently, buildout.cfg etc. have to live in the repository root, unless I am missing something.
• Currently, I have to give the target machine read access to my buildout repository. Pushing the buildout from the control machine seems better from a security point of view.

[rfleschenberg]

If you agree that this would be nice to have, I can volunteer to submit a PR.

And I forgot to say: thank you for your work on this project!