[k8s] improve test-coverage for experimental k8s integration

[thaJeztah]

relates to #721

Current coverage is low (partly related to the generated code, which should likely be excluded), but we should improve coverage before the feature leaves experimental

/cc @dnephin @vdemeester @silvin-lubecki

[dnephin]

The generated code should be excluded from this count, but I'm not sure that codecov re-ran after the config was updated.

[thaJeztah]

kubernetes integration was deprecated and removed; let me close this one