Improve post-mortem data available via RM

The status information available from RM is weaker than that available from AM.
Perhaps rich status from AM can be bundled into a protobuf packet (or JSON) and pushed to RM during shutdown.
eg during shutdown, set appMessage=

{AppMaster status + <diagnostic messages>}

in parsable format.

Then the client-side code can be: get StatusInfoPacket from either AM or RM. decode packet and populate client-side structures.