Ensemble branch option needs to allow for distro pkg, ppa, and source branch install

Excerpts from Kapil Thangavelu's message of Wed Aug 17 16:17:46 UTC 2011:
> Public bug reported:
>
> Ensemble currently defines an ensemble-branch environment option which
> allows specification of where to get ensemble code for machine
> deployments (limited to bzr published branches). At the moment we
> default to ppa package installation if this option is not specified.
>
> Its critical for the oneiric rellease that we have a mechanism that
> defaults to using the distro package, but allows specifying the ppa, or
> a branch. This should also rename the 'ensemble-branch' option to
> 'ensemble-origin'.

Can solve this and allow for private hosting by making ensemble-origin
flexible as either a branch (lp:xxx), a ppa:xxx, or an apt sources line:

ensemble-origin: "deb http://mymirror.internal/ubuntu oneiric main"
ensemble-version: 0.5+306-0ubuntu1

ensemble-origin: lp:ensemble
ensemble-version: 306

ensemble-origin: ppa:ensemble/ppa

Unspecified version should always mean the "latest available".

On a "higher order" note, I wonder if, for repeatability, we shouldn't
process all of this on the client side, and just build a deb or tarball
that is pushed into file storage.

Hi guys,

This bug is release-critical for Ubuntu 11.10 JuJu for us... Can we get an update as to where we are with it? We require JuJu to default to bootstrapping and installing the distro JuJu package on bootstrap and service nodes. Leaving the features to pull JuJu from a bzr branch or a ppa would be a nice to have. Thanks.

I believe Clint is working on having this addressed for 11.10.

This branch is pretty critical for the final release. I did take a look at making the default _DISTRO in the distro packages, but it ripples through too much code and affects too many tests. The branch looks to be nearly ready for merge into trunk, so I'm confident we'll have it in 11.10.