rpc: include structured error information in responses
    
    Include keyword arguments of exceptions in RPC responses. This is limited
    to JSON-RPC, as XML-RPC does not support additional data in error
    responses.
    
    Include keyword arguments of messages in RPC responses.
    
    Include keyword arguments of exceptions in batch command result.
    
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: David Kupka <dkupka@redhat.com>