Add subnets to the resource list

[JerJon]

Fixes #737

Loping through all the "main" resources and get all the subnets for each Vnet that has been found.

This function can be expand for other sub-resources that aren't been retrieved by the Rest-Api "Resources"

[JerJon]

@microsoft-github-policy-service agree

[anwather]

I just want to test this and make sure there isn't a huge impact to performance