WIP: Basic heartbeat passthru

Just want some feedback to see if this is a decent way to deal with heartbeating in the driver.

There are 3 possibilities for the node's state when it heartbeats:
* first time the node is ever heartbeating: add the node
* node just rebooted (either deliberately moving to decom, or unexpectedly, doesn't know its uuid yet): tell it what its target state is
* node is checking in with uuid while currently doing decom/standby: update db so we can know when it dies.