Rework update agent communication

During implementing a docker update feature using the [AKTIN Updateagent](https://github.com/aktin/debian-updateagent-pkg), @rwm and I @LongusBongus decided to rework the communication. Currently communication runs as fire and forget requests, not we want to use keep-alive connections. For that @akomii proposed switching tcp, because of lower code overhead for implementation.

For that find a minimal invasive communication architecture, to keep the current functions as is but supporting the new unix sockets.

Sub-issues in other repository:
- https://github.com/aktin/debian-updateagent-pkg/issues/16