Enhance EdgeGateway datasource by returning interface information.

[jamiejarmstrong]

Version:
2.5

Scenario
In our environment when a new Edge Gateway is attached to an External Network, the subnet info (netmask, ip, gateway) for the Edge's uplink interface is assigned at random after creation.

Problem:
Currently, the Edge Gateway data source does not return interface(s) subnet information beyond the "uplink" name (which is returned in the "external_networks" list). This prevents us being able to create new D/SNAT rules for an Edge as the IP of the uplink must be known, and cannot be retrieved after EGW creation using the data source or resource.

Proposed Solution:
Add new elements to datasource_vcd_edgegateway.go Schema that contain netmask, ip, gateway for each interface on the EGW. These values are available in the existing SubnetParticipation type, and just need to be mapped to a new element on the data source. I'm not that familiar with the inner workings of the provider yet, so I'm not sure if this change would/could also apply to the resource itself, as shown below I'm just using the data source for now. A nested set/map of each interface's subnet info would be ideal, however simply adding new lists for external_netmask, external_ip, external_gateway would suffice as we could use the index of external_networks to lookup the corresponding subnet info.

Current Workaround
I'm currently able to achieve what I want by duplicating the "external_networks" element, and its associated logic; I tried a more robust method but struggled with the XML Types and nesting maps/sets in Go (I'm fairly new to both!).

resource_vcd_edgegateway.go - line 323

	var networks []string
	var external_ips []string //My new string array
	for _, net := range egw.EdgeGateway.Configuration.GatewayInterfaces.GatewayInterface {
		if net.InterfaceType == "uplink" {
			networks = append(networks, net.Network.Name)
			gateways[net.SubnetParticipation.Gateway] = net.Network.Name
			external_ips = append(external_ips, net.SubnetParticipation.IPAddress) //Add gateway interface IP to array
		}
	}
	err = d.Set("external_networks", networks)
	err = d.Set("external_ips", external_ips)` //set value on object

Schema addition in datasource_vcd_edgegateway.go

"external_ips": &schema.Schema{
				Type:        schema.TypeList,
				Computed:	true,
				Description: "A list of external ips used by the edge gateway",
				Elem: &schema.Schema{
					Type: schema.TypeString,
				},
			},

I can then retrieve the external_ip of a gateway resource using the below:

data "vcd_edgegateway" "mygw" {
    name = "Edge_LAN1"
    org = "TEST"
    vdc = "TESTVDC"
}

output "test1" {
  value = data.vcd_edgegateway.mygw.external_ips
}

[jamiejarmstrong]

Duplicate of #308