Make the non ha router usage explicit in a dvr test

Neutron has a non dvr, ha mode which can be a default (by
 l3_ha = True) option for all router creation.

test_centralized_router_update_to_dvr admin test case
needs to define an additional option in order to
get a `legacy` non ha router in the initial step.

Change-Id: Ib262f32133aae50cdb01d2489830499fb5c30f44
diff --git a/tempest/api/network/admin/test_routers_dvr.py b/tempest/api/network/admin/test_routers_dvr.py
index 36cb15f..7de3760 100644
--- a/tempest/api/network/admin/test_routers_dvr.py
+++ b/tempest/api/network/admin/test_routers_dvr.py
@@ -95,9 +95,11 @@
         """
         name = data_utils.rand_name('router')
         # router needs to be in admin state down in order to be upgraded to DVR
+        # l3ha routers are not upgradable to dvr, make it explicitly non ha
         router = self.admin_routers_client.create_router(name=name,
                                                          distributed=False,
-                                                         admin_state_up=False)
+                                                         admin_state_up=False,
+                                                         ha=False)
         self.addCleanup(self.admin_routers_client.delete_router,
                         router['router']['id'])
         self.assertFalse(router['router']['distributed'])