Code review comment for ~chad.smith/cloud-init:feature/os-local

I would rather you push 'doc: scrub ec2, ...'' as a separate merge proposal.

I dont want to make busywork, but contained commits make things easier.

Other than that I have only a nitpick on the name 'use_network_json'.
It would seem more "datasource generic" if we named it "apply_network_config" or something.
then this same variable could at least conceptually be used on other datasources.