Fix convert

[tnozicka]

This fixes object serialization and writing objects in convert. It was a FIXME and it didn't work until this PR.

This PR will help us move forward a lot because it allows us to actually output deployable objects.

For reviewers:

It took me several hours to find the 4 magic lines by digging in Kubernetes sources; definitely no docs :(

import (
    api_v1 "k8s.io/client-go/pkg/api/v1"
)

scheme := runtime.NewScheme()
api_v1.SchemeBuilder.AddToScheme(scheme)
versionedObject, err := scheme.ConvertToVersion(runtimeObject, api_v1.SchemeGroupVersion)

This can't really break anything as it didn't work before :D
But I have tested it manually and we should cover it once we have E2E tests.