breaking change: repository structure, deploy interface

[William Reade]

On Wed, 2011-09-28 at 23:31 -0700, Clint Byrum wrote:
> This default selection based on the local machine series seems
> totally arbitrary.  While we hope the world runs Ubuntu, the reality
> is that many of our users will be using juju from OS X, or maybe even
> Fedora/CentOS/RHEL... FreeBSD maybe?
> 
> I think we can safely set the default series to just 'oneiric' and when
> the next series is "released" in the charm repository, bump the default
> in juju to that, noting the update. Making this so dynamic will, I think,
> harm repeatability of deployments.

I'm not sure that bumping the default-series will actually be any less
harmful to repeatability. I guess it will probably happen less often,
but I think that repeatability would demand that we make it a required
key.

What if we made it required, and changed the default environments.yaml
(that gets generated if it doesn't already exist) to include a
default-series of "oneiric"? We can update that as and when we please
without changing anyone's existing environment.