InternalCommandPortListeningCheck always fails for containers built without `/bin/sh`

Relates to #2984

I'm surprised we've not come across this earlier, but the default TCP port listening detector InternalCommandPortListeningCheck does not work for containers that do not have /bin/sh included.

This predominantly affects images built upon scratch.

The workaround/solution is to use a more application specific WaitStrategy - e.g. an HTTP wait strategy.

However the log messages don't make this easy to realise.

Given that we do both the internal and external port checks for a good reason, I don't think we can just rely on the external port check. Still perhaps we can raise a very specific error message if /bin/sh is not available inside the container.

Beginne mit InternalCommandPortListeningCheck und verfolge den Log- und Fehlerpfad, der verwendet wird, wenn einem Container /bin/sh fehlt. Reproduziere das Verhalten mit einem von scratch erstellten Image und sorge dann dafür, dass der Fehler die fehlende Shell und die betroffene Wartestrategie eindeutig angibt.