Draft: Leave endpoint hostname empty if it does not resolve

If the hostname does not resolve to a valid IP address the function from the system package reports "0.0.0.0". In this case we leave endpoint host/ip part empty to fall back to the default behaviour.

Seen by remote institue running tdaq-12 locally. Waiting for confirmation that the suspected cause of failure is indeed correctly diagnosed.

Like !13 (merged) will also be needed for tdaq-12-00-00.