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.

InternalCommandPortListeningCheck から始め、コンテナに /bin/sh がない場合に使用されるログとエラーの経路をたどります。scratch からビルドしたイメージで動作を再現し、その後、失敗時に不足しているシェルと影響を受ける待機戦略が明確に示されるようにします。