[Network] Vnet-gateway update issues

[aanandr]

1. The arguments for the two are very different. Python provides a generic way to specify objects but JS doesnt have this capability. As a result, in JS, there is no way to set BGP settings
2. Python doesnt have settings for SKU
3. Why does Python have address-prefixes param? It is not there in powershell. It is not needed
4. Both versions should have params for BGP and other settings. Just specifying an object is not enough

[tjprescott]

Issues with Xplat (Node) should be filed separately here: https://github.com/Azure/azure-xplat-cli

[tjprescott]

@aanandr
By (2) do you mean that capacity is not exposed? Is there ever an instance where name and tier would not be the same?

IRT (3) address-prefixes is present, according to the help, because it is a prerequisite for uploading certificates. Is this not the case?

[tjprescott]

Our action items:

• Add BGP peering settings to create and update (just like with local-gateway)
  - [ ] Add SKU capacity
• Add missing UltraPerformance SKU type