Update client data (for JIT Clients)

[EvilGrinUK]

I have a bunch of checks that use 'source' for devices on my network that can't run a sensu client (SANs, switches, firewalls, etc). I'd like to be able to use sensu-cli to amend the address and subscriptions for these clients.

[agent462]

This is coming soon. I've been playing around with some refactoring so I've been debating on pushing this in now or waiting to see how the progress on the refactoring goes.