fix get the name servers for a zone not validate zone_id

now the api of get /v2/zones/{zone_id}/nameservers not validate zone_id,
if set zone_id contain spaces, will trigger DBError and return 500.

Change-Id: Ia3e07c42dc548207aa7ff9efcc35a215c9660e54
(cherry picked from commit 0ba52bfb62)

designate/api/v2/controllers/zones/nameservers.py

@@ -16,6 +16,7 @@
 import pecan
 from oslo_log import log as logging
 
+from designate import utils
 from designate.api.v2.controllers import rest
 from designate.objects.adapters import DesignateAdapter
 
@@ -25,6 +26,7 @@ LOG = logging.getLogger(__name__)
 class NameServersController(rest.RestController):
 
     @pecan.expose(template='json:', content_type='application/json')
+    @utils.validate_uuid("zone_id")
     def get_all(self, zone_id):
         """List NameServers for Zone"""
         request = pecan.request