[r=dimitern] Show networks in juju status
This adds a new state method AllNetworks(), which returns
all networks in state, and also makes the necessary changes
to the API and cmd/juju so we can show networks as top-level
entities in juju status:
machines: ...
services: ...
networks:
net1:
provider-id: foo
cidr: 0.1.2.0/24
vlan-tag: 42
https://codereview.appspot.com/91000043/
R=hduran-8