New Go juju command

[Ian Booth]

Hi

You will want to update both juju-core and Goose next time you decide to bzr pull.
In so doing, there is a new juju command (see bug 993616)

juju generate-config [-w]

With no arguments, the command will generate a boilerplate config which contains sections for each registered provider. 
The config parses, and in the case of openstack, just needs the default instance id to be filled in. So it's a good way of
getting going quickly.

With the -w argument, if there is not currently a ~/.juju/environments.yaml, the boilerplate config will be written to the 
file instead of stdout.

As local and MAAS providers are added, the provider's BoilerplateConfig() method needs to be written to provide the config
block for the provider.