This moves node ping controller to using the new internal lock
API.
The reason for this is twofold:
* The channel approach that was used to notify other
controllers of changes could only be used once (at startup),
and couldn't be used in the future to broadcast node
ping status. The idea idea is here that we could move
to a sync.Cond style API and only wakeup other controllers
on change, as opposed to constantly polling each other
* The problem with sync.Cond is that it's not context friendly.
If we want to do stuff like wait on a sync.cond and use a context
or a timer or similar, it doesn't work whereas this API allows
context cancellations on condition change.
The idea is that as we have more controllers that act as centralized
sources of authority, they can broadcast out their state.
