support optional extra config for bundle deployments

[Richard Harding]

Per Kapil the deployer supports an optional config.yaml when deploying a bundle so that you can generate a set of overriding config params to the bundle you deploy.

It's been requested that quickstart support passing this config down to the deployer as well.

[David Britton (dpb)]

Being able to selectively override on the command line with the following syntax (or similar) would also be highly desireable:

   --service-option "<service>:key=value"

Would make it simple to (for instance):

  * set the debug level of a deployed service
  * adjust the initial deployed software to a newer or older version as desired

Etc...

[David Britton (dpb)]

also, adjust the port of juju-gui, which is currently impossible with quickstart.