datasource: use opaque object instead of string

Rather than serializing the network config into a string and then later
deserializing it, just pass the object through directly.

datasource/metadata/digitalocean/metadata.go

@@ -100,7 +100,7 @@ func (ms *metadataService) FetchMetadata() (metadata datasource.Metadata, err er
 	for i, key := range m.PublicKeys {
 		metadata.SSHPublicKeys[strconv.Itoa(i)] = key
 	}
-	metadata.NetworkConfig = data
+	metadata.NetworkConfig = m
 
 	return
 }

datasource/metadata/digitalocean/metadata_test.go

@@ -90,34 +90,27 @@ func TestFetchMetadata(t *testing.T) {
 					"0": "publickey1",
 					"1": "publickey2",
 				},
-				NetworkConfig: []byte(`{
-  "droplet_id": 1,
-  "user_data": "hello",
-  "vendor_data": "hello",
-  "public_keys": [
-    "publickey1",
-    "publickey2"
-  ],
-  "region": "nyc2",
-  "interfaces": {
-    "public": [
-      {
-        "ipv4": {
-          "ip_address": "192.168.1.2",
-          "netmask": "255.255.255.0",
-          "gateway": "192.168.1.1"
-        },
-        "ipv6": {
-          "ip_address": "fe00::",
-          "cidr": 126,
-          "gateway": "fe00::"
-        },
-        "mac": "ab:cd:ef:gh:ij",
-        "type": "public"
-      }
-    ]
-  }
-}`),
+				NetworkConfig: Metadata{
+					Interfaces: Interfaces{
+						Public: []Interface{
+							Interface{
+								IPv4: &Address{
+									IPAddress: "192.168.1.2",
+									Netmask:   "255.255.255.0",
+									Gateway:   "192.168.1.1",
+								},
+								IPv6: &Address{
+									IPAddress: "fe00::",
+									Cidr:      126,
+									Gateway:   "fe00::",
+								},
+								MAC:  "ab:cd:ef:gh:ij",
+								Type: "public",
+							},
+						},
+					},
+					PublicKeys: []string{"publickey1", "publickey2"},
+				},
 			},
 		},
 		{