Before the drain CLI would block until the node was marked as completing
drain operations. While technically correct, it could lead operators (or
more likely: scripts) to shutdown drained nodes before all of its
allocations had *actually* terminated.
This change makes the CLI block until all allocations have terminated
(unless ignoring system jobs).
Also delay "node complete" after the node has been marked complete to
capture a few more alloc events. There are other ways to implement this
that could trade off correctness for responsiveness as technically a
node is considered drained when all of its allocs have been marked to
stop and not when they've actually stopped (which may not happen for a
long time).
* Truncate all UUID identifiers to eight characters by default
* Refactor the node identifier to an auto-generated UUID
* Created and updated tests and mocks
