minor iostreams error handling improvements

	modified:   src/bruce/batch/per_topic_batcher.test.cc
	modified:   src/bruce/batch/single_topic_batcher.test.cc
	modified:   src/bruce/conf/conf.cc
	modified:   src/bruce/mock_kafka_server/inject_error/inject_error.cc
	modified:   src/bruce/mock_kafka_server/server.cc
	modified:   src/bruce/mock_kafka_server/setup.cc
	modified:   src/bruce/mock_kafka_server/setup.h
	modified:   src/bruce/mock_kafka_server/single_client_handler_base.cc
	modified:   src/bruce/mock_kafka_server/single_client_handler_base.h
	new file:   src/bruce/util/exceptions.cc
	new file:   src/bruce/util/exceptions.h