Add V3 API Test to get the VNC console of server

This patch adds V3 API Test to get the VNC console of server

Change-Id: I120163d0821eb7d8b2d62000be7cdd991925c341
diff --git a/tempest/services/compute/v3/json/servers_client.py b/tempest/services/compute/v3/json/servers_client.py
index 840e914..819e366 100644
--- a/tempest/services/compute/v3/json/servers_client.py
+++ b/tempest/services/compute/v3/json/servers_client.py
@@ -423,3 +423,15 @@
     def restore_soft_deleted_server(self, server_id, **kwargs):
         """Restore a soft-deleted server."""
         return self.action(server_id, 'restore', None, **kwargs)
+
+    def get_vnc_console(self, server_id, type):
+        """Get URL of VNC console."""
+        post_body = json.dumps({
+            "get_vnc_console": {
+                "type": type
+            }
+        })
+        resp, body = self.post('servers/%s/action' % str(server_id),
+                               post_body)
+        body = json.loads(body)
+        return resp, body['console']