[r=dimitern],[bug=1323263] cmd/juju: Fixes #1323263: drop --exclude-networks
Removed --exclude-networks argument from juju deploy CLI.
Also fixed the command help text.
In a follow-up, after we introduce network constraints,
the ability to specify what networks to exclude will
be restored.
For now, we just need to drop the CLI argument, as it
was decided we don't need it, and needs to be done
before the next release.
https://codereview.appspot.com/101820044/
R=mfoord