[FlightRPC][Java] FlightStream should unwrap ExecutionExceptions

[asfimport]

Currently FlightStream bubbles a lot of exceptions as RuntimeException or ExecutionException, or just wraps them with CallStatus.INTERNAL. For RuntimeException, we should always check if it's a gRPC StatusRuntimeException and convert to the equivalent Flight exception; for ExecutionException, we should check if the cause is a gRPC exception and convert.

Example: on master, FlightStream#getDescriptor reports all errors as CallStatus.INTERNAL, but we should inspect ExecutionException#getCause instead.

This is needed so that errors get properly reported, e.g. if a service sends a PERMISSION_DENIED error, the client should get that and not a RuntimeException, ExecutionException, or INTERNAL error.

Reporter: David Li / @lidavidm
Assignee: David Li / @lidavidm

_{Note: This issue was originally created as ARROW-8879. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
This was already fixed in 1.0.0 when FlightStream was refactored for DoExchange.