Test backend logging output gives no mention that site is ready for testing

[ichim-david]

Using Volto from the main branch and trying to setup the cypress testing by following the guide from https://6.docs.plone.org/volto/contributing/acceptance-tests.html#how-to-run-acceptance-tests-locally-during-development You end up with this experience: You don't get any ready flag, just an error that plone.app.event is already added. You get some info about the backend only when you ctrl + c as seen in my screenshot.

Going to http://localhost:55001/ will show you a lovely we're sorry message A normal plone start would show you the plone setup screen where you see that you have a plone site up and running and you could click to take you to http://localhost:55001/plone

This makes you believe that the backend is broken when in fact it works if you know to visit then http://localhost:55001/plone

[davisagli]

Related fixes:

1. https://github.com/plone/plone.app.robotframework/pull/154 avoids the warning about installing plone.app.event
2. https://github.com/plone/plone.app.robotframework/pull/155 fixes printing the server URL
3. https://github.com/plone/volto/pull/5748 makes sure the output is not buffered.