Make local network gateways tests pass

[jen20]

This diff represents the changes necessary to make local network gateway tests pass:

• Parse the resource ID instead of relying on attributes
• Remove unecessary logging (which is handled via the autorest wrapper)
• Resource GUID is removed - if this is actually required for anything we may need to find a way to supress it during apply, as we get spurious diffs in plans otherwise.
• Various typos fixed.

Output from the acceptance tests:

make testacc TEST=./builtin/providers/azurerm TESTARGS="-run AzureRMLocalNetworkGateway"
go generate ./...
TF_ACC=1 go test ./builtin/providers/azurerm -v -run AzureRMLocalNetworkGateway -timeout 90m
=== RUN TestAccAzureRMLocalNetworkGateway_basic
--- PASS: TestAccAzureRMLocalNetworkGateway_basic (56.98s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/azurerm    56.995s

[aznashwan]

Hey; my apologies for the delays...
Everything looks like a great catch; merging and updating hashicorp#4342 now.