VCS code duplication and subordinate

[Patrick Hetu]

In the process of building the Django charm, I realized that a lot of charms are
repeating the parts that handle VCS. Like:

  http://bazaar.launchpad.net/~charmers/charms/precise/node-app/trunk/view/head:/hooks/install#L28
  http://bazaar.launchpad.net/~charmers/charms/precise/rack/trunk/view/head:/hooks/install#L38
  http://bazaar.launchpad.net/~charmers/charms/precise/python-django/trunk/view/head:/hooks/install#L36

There is also a blueprint here:

  https://blueprints.launchpad.net/juju/+spec/juju-charm-app-git-deployment

So, I was thinking that we could create one subordinate charm per VCS to:

1) Reduce the installation time
2) Ease the maintenance
3) Include more advance stuff like branches, authentification, etc

What do you think?

Patrick