Graceful shutdown if athena process is killed while running browser tests

[caiomoritz]

It's not uncommon that a developed, while running a project tests locally, will have the need to stop a long running Behat test suite in the middle. The only way to do this currently is to send the Athena process a kill signal (by using kill or simply Ctrl C on a foreground process).

The problem is that it's impossible to run the exact same command again without restarting all containers (because of Proxy and/or Selenium Hub). Any subsequent test will fail with a timeout (the proxy won't respond anymore).

Ideally, either the plugin or athena would be able to process the shutdown signal and gracefully kill or restart the Proxy and Selenium Hub containers, so that the developer doesn't need to.