Handle cases of bad parent/child modelling

[alex-frankel]

Cases where a resource (i.e. subnets) is modelled as both a child resource and as a property of the parent resource. This effectively tricks what-if into thinking the resource exists/could exist in both places because the VNET will return subnet info in it's GET response AND we can GET the resource directly as a child resource.

[alex-frankel]

Customer reported examples:

• Microsoft.Network/networkSecurityGroups #60
• Microsoft.Network/virtualNetworks (2019-11-01) #46
• Microsoft.ContainerService/managedClusters #128?

[shenglol]

#140