nuageinit: Allow the use of network parameters from network-config

[dtxdf]

Summary

To better comply with the cloud-init specification, we need to support the configuration of network-related parameters from the network-config file, which is common in most deployments.

[dtxdf]

• Remove unneeded parameter from parse_network_config(...).

[bapt]

Consider adding your copyright at some point, you have done some significant additions to the code ;)