Proposed API Change - Get default repo/namespace from environment variable.

[Kapil Thangavelu]

Excerpts from Gustavo Niemeyer's message of 2012-02-28 17:31:05 -0500:
> Hey Clint,
> 
> > This allows us to not have to wrap juju in so intrusive a way. We can
> > just run the test script with special environment variables. So:
> >
> > export JUJU_REPOSITORY=/path/to/testing/repo
> 
> That sounds reasonable.
> 
> > export JUJU_CHARM_NAMESPACE=local
> 
> Sounds reasonable too, but I suggest that we call it JUJU_DEFAULT_NS,
> and allow it to take one of the following forms:
> 
> 1) scheme: (not "scheme" without colon.. that's potentially ambiguous
> with series)
> 2) scheme:series or scheme:series/ (e.g. local:oneiric, or cs:oneiric/)
> 3) scheme:~user/series, or scheme:~user/series/ (e.g. cs:~spamaps/oneiric/)
> 
> If the variable is set, it will alter the way that charm names are
> resolved when information is missing (no scheme, or no series). The
> resolution algorithm should use the provided values and follow up from
> there as it would for the values still missing.
> 
> How does that sound to everybody?

Series is a little different. Its specified/required in the environments.yaml.
The other options here are just additional parameterization of existing cli 
options. Mixed series implies somethings which we haven't really done much with 
yet, namely, mixed release environments, possibly running mixed version of 
juju.

ie. including series means collapsing two configuration items into a single 
value, that may conflict with something else already set. We can detect and 
warn/error on conflict, but given that its a required atm, its not clear that 
has any real value outside of creating the possibility of conflicts.

> 
> > One side note, I didn't find a good place to document these environment
> > variables.  Perhaps we can resurrect the man page, or find a place in
> > docs/source for it.
> 
> I suggest putting that documentation in the command help (e.g. juju
> deploy --help should show it), in addition to the online docs.

sounds good.

cheers,

Kapil