[r=dimitern] cmd/juju: Add --(exclude-)networks args to deploy
Implemented two new arguments to juju deploy:
--networks and --exclude-networks. They allow specifying
networks to enable/disable when deploying new machines
hosting units of the service.
If the API server is older than 1.17.7 and does not
support ServiceDeployWithNetworks, and networks are
specified, an error is returned. Otherwise (without
networks specified), the command falls back to using
ServiceDeploy API.
https://codereview.appspot.com/80600044/
R=jameinel