test: Extract a common "netns service" base class

[wkz]

Description

We have a bunch of things that create processes that run inside a netns (DHCP servers, tcpdump instances etc.)

These share a bunch of behavior:

• Creates and manages a subprocess (with proper termination semantics etc.)
• Should be usable as context managers
• Should be usable with explicit .start()/.stop() methods
• ...maybe more?

It would be good if we had a common implementation for this.

Additional Information

No response

General Information

Anyone can help out by sponsoring development of new features or contributing pull requests. Please use this issue for discussions related to the feature.