Add support for sovereign environments in Azure networking modules

[mjyeaney]

The network interface and network security group testing modules need modified to support Azure sovereign environments (if configured). This will require:

• Addition of new supporting methods in /modules/azure/client_factory.go for NIC and NSG clients.
• Modifying /modules/azure/networkinterface.go and /modules/azure/nic.go to call into client_factory.go to ensure client instances are properly configured.
• Updating any tests impacted.

Will submit PR on this work when complete.