juju: add UpdateEnvironConfig

juju: add UpdateEnvironConfig

This is not a proposal. This is an aide for the discussion
about pushing the secrets.

https://code.launchpad.net/~dave-cheney/juju-core/go-juju-update-environment/+merge/116610

(do not edit description out of merge proposal)

[niemeyer, 2012-07-25 10:05:52]

https://codereview.appspot.com/6445045/diff/1/environs/open.go
File environs/open.go (right):

https://codereview.appspot.com/6445045/diff/1/environs/open.go#newcode22
environs/open.go:22: // Config returns the *config.Config associated with the
environ
// Config returns the environment configuration with the given name.

https://codereview.appspot.com/6445045/diff/1/environs/open.go#newcode30
environs/open.go:30: }
p, ok := providers[config.Type()]
if !ok {
    return nil, fmt.Errorf("no registered provider for %q", config.Type())
}
return p.Validate(e.config, nil)