provider/azurerm: azurerm_dns_zone now returns name_servers

Fixes #7374

The introduction of the AzureRM SDK 3.0.0-beta means that the
`name_servers` for the DNS Zone are returned from the API

This PR has a dependency on #7420 being merged first

```
make testacc TEST=./builtin/providers/azurerm TESTARGS='-run=TestAccAzureRMDnsZone_'
==> Checking that code complies with gofmt requirements...
/Users/stacko/Code/go/bin/stringer
go generate $(go list ./... | grep -v /vendor/)
2016/06/30 15:20:01 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/azurerm -v
-run=TestAccAzureRMDnsZone_ -timeout 120m
=== RUN   TestAccAzureRMDnsZone_basic
--- PASS: TestAccAzureRMDnsZone_basic (92.42s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/azurerm
92.444s
```

builtin/providers/azurerm/resource_arm_dns_zone.go

@@ -39,6 +39,13 @@ func resourceArmDnsZone() *schema.Resource {
 				Optional: true,
 				Computed: true,
 			},
+
+			"name_servers": &schema.Schema{
+				Type:     schema.TypeSet,
+				Computed: true,
+				Elem:     &schema.Schema{Type: schema.TypeString},
+				Set:      schema.HashString,
+			},
 		},
 	}
 }
@@ -104,6 +111,14 @@ func resourceArmDnsZoneRead(d *schema.ResourceData, meta interface{}) error {
 	d.Set("number_of_record_sets", resp.NumberOfRecordSets)
 	d.Set("max_number_of_record_sets", resp.MaxNumberOfRecordSets)
 
+	nameServers := make([]string, 0, len(resp.NameServers))
+	for _, ns := range resp.NameServers {
+		nameServers = append(nameServers, *ns)
+	}
+	if err := d.Set("name_servers", nameServers); err != nil {
+		return err
+	}
+
 	return nil
 }
 

vendor/vendor.json

@@ -951,32 +951,32 @@
 		{
 			"checksumSHA1": "oPpOfZn11Ef6DWOoETxSW9Venzs=",
 			"path": "github.com/jen20/riviera/azure",
-			"revision": "2f01b8f5b09bbc20a591b1dc4b48af0665106b3f",
-			"revisionTime": "2016-06-10T12:18:12Z"
+			"revision": "1159d86fc8144abafeb29ee7c5a3e2e85af336ba",
+			"revisionTime": "2016-06-30T14:11:29Z"
 		},
 		{
-			"checksumSHA1": "A2Ycn6MySifUKTHOnsG9oLwjitE=",
+			"checksumSHA1": "ncdT+1PFEF5ly0niXuQc9/pKzT0=",
 			"path": "github.com/jen20/riviera/dns",
-			"revision": "2f01b8f5b09bbc20a591b1dc4b48af0665106b3f",
-			"revisionTime": "2016-06-10T12:18:12Z"
+			"revision": "1159d86fc8144abafeb29ee7c5a3e2e85af336ba",
+			"revisionTime": "2016-06-30T14:11:29Z"
 		},
 		{
 			"checksumSHA1": "zVXx6ha3bt0N4ukRbRHXjSl91S4=",
 			"path": "github.com/jen20/riviera/search",
-			"revision": "2f01b8f5b09bbc20a591b1dc4b48af0665106b3f",
-			"revisionTime": "2016-06-10T12:18:12Z"
+			"revision": "1159d86fc8144abafeb29ee7c5a3e2e85af336ba",
+			"revisionTime": "2016-06-30T14:11:29Z"
 		},
 		{
 			"checksumSHA1": "KfquDaeBPGchw92QnojlJFsJKgk=",
 			"path": "github.com/jen20/riviera/sql",
-			"revision": "2f01b8f5b09bbc20a591b1dc4b48af0665106b3f",
-			"revisionTime": "2016-06-10T12:18:12Z"
+			"revision": "1159d86fc8144abafeb29ee7c5a3e2e85af336ba",
+			"revisionTime": "2016-06-30T14:11:29Z"
 		},
 		{
 			"checksumSHA1": "nKUCquNpJ9ifHgkXoT4K3Xar6R8=",
 			"path": "github.com/jen20/riviera/storage",
-			"revision": "64de55fa8cdd0c52f7d59494c1b03c1b583c52b4",
-			"revisionTime": "2016-02-18T23:50:40Z"
+			"revision": "1159d86fc8144abafeb29ee7c5a3e2e85af336ba",
+			"revisionTime": "2016-06-30T14:11:29Z"
 		},
 		{
 			"comment": "0.2.2-2-gc01cf91",