Code review comment for lp:~gz/juju-core/addservice_using_networks

LGTM, with one improvement: when no networks are to be given to a
service, passing nil instead of []string{} is better (for both args).

https://codereview.appspot.com/79800043/diff/1/cmd/juju/status_test.go
File cmd/juju/status_test.go (right):

https://codereview.appspot.com/79800043/diff/1/cmd/juju/status_test.go#newcode1629
cmd/juju/status_test.go:1629: _, err := ctx.st.AddService(as.name,
"user-admin", ch, []string{}, []string{})
Just passing nil, nil should be enough.

https://codereview.appspot.com/79800043/diff/1/environs/jujutest/livetests.go
File environs/jujutest/livetests.go (right):

https://codereview.appspot.com/79800043/diff/1/environs/jujutest/livetests.go#newcode455
environs/jujutest/livetests.go:455: svc, err :=
conn.State.AddService("dummy", "user-admin", sch, []string{},
[]string{})
ditto (and all other places)

https://codereview.appspot.com/79800043/