Support Docker private registry for Kubernetes cluster with MgmtDriver

The sample MgmtDriver for Kubernetes cluster VNF supports only Images
registered in the Docker public registry but doesn't support ones in
Docker private registry. For use-case in Network Operators, it is assumed
that their Images are not in public but in their local repository.

This specification enables the use of Docker private registry images for
Kubernetes cluster VNF. The sample MgmtDriver supports to configure
eatch node in the cluster to access the Docker private registry.
The local registry is called Container Image Registry (CIR) in ETSI NFV
specifications.