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).
This PR allows marking a node as eligible for scheduling while toggling
drain. By default the `nomad node drain -disable` commmand will mark it
as eligible but the drainer will maintain in-eligibility.
This PR enhances the API package by having client only RPCs route
through the server when they are low cost and for filesystem access to
first attempt a direct connection to the node and then falling back to
a server routed request.
* Truncate all UUID identifiers to eight characters by default
* Refactor the node identifier to an auto-generated UUID
* Created and updated tests and mocks
