Make test_volume_quotas force tenant isolation

The test requires tenant isolation but wasn't forcing it with the
force_tenant_isolation attribute.

Closes-Bug: #1291409

Change-Id: I0fcfb2832489249c723ced0d9001fb0b5a3d331f
diff --git a/tempest/api/volume/admin/test_volume_quotas.py b/tempest/api/volume/admin/test_volume_quotas.py
index 31f6730..742f7e1 100644
--- a/tempest/api/volume/admin/test_volume_quotas.py
+++ b/tempest/api/volume/admin/test_volume_quotas.py
@@ -23,6 +23,7 @@
 
 class VolumeQuotasAdminTestJSON(base.BaseVolumeV1AdminTest):
     _interface = "json"
+    force_tenant_isolation = True
 
     @classmethod
     def setUpClass(cls):