DRILL-3714: Avoid cascading disconnection when a single connection is broken.
- Move the coordination id management to be connection level instead of RpcBus level
- Rename CoordinationQueue to a more appropriate name: RequestIdMap
- Simplify locking and memory overhead of RequestIdMap. It used to be that this would accessed by a large number of threads concurrently. We modified the behavior so that it is only accessed by two threads at most. Rather than have memory overhead of ConcurrentHashMap, switch to simple locking approach since contention should be low.
- Update all methods associated with coordination to improve names as well as add javadocs. Move these methods to the RemoteConnection.
- Consolidate the two different close handlers into a single, ordered close handler managed inside the connection.
- Add better javadoc around the close method of RemoteConnection
- Add some preconditions checks.
- Update the HPPC version in the base memory module since it conflicts with the one in the java-exec module.
This closes #463.
