Add return type to MessageQueue command execute method - #222

Declaration of Magento\MessageQueue\Console\QueueConfigStatusCommand::execute(Symfony\Component\Console\Input\InputInterface $input,
  Symfony\Component\Console\Output\OutputInterface $output) must be compatible with Symfony\Component\Console\Command\Command::execute(Symfony\Component\Console\Input\InputInterface
  $input, Symfony\Component\Console\Output\OutputInterface $output): int