Avoid duplicating tenant check when creating resources

The check of the tenant done in the method _get_tenant_id_for_create()
is already did by the Neutron Controller in prepare_request_body(),
with a call to attributes.populate_tenant_id().
Moreover, when the Controller processes a "create" requests, it
will add the 'tenant_id' to the resource dict.
Thus, _get_tenant_id_for_create() can be deleted.
Calls to this method are replaced by the res['tenant_id'].

Changes have to be done in UT to explicitly add the tenant_id while
creating resources, since the UT framework is bypassing the controller code
that automatically adds the tenant_id to the resource.

Co-Authored-By: Hong Hui Xiao <xiaohhui@cn.ibm.com>
Closes-Bug: #1513825
Change-Id: Icea06dc81344e1120bdf986a97a6b1094bbb765e
Depends-On: I31022e9230fc5404c6a94edabbb08d2b079c3a09
Depends-On: Iea3f014ef17a1e1b755cd2efe99afd1a36ebbc6a
Depends-On: I604602d023e0cbf7f6591149f914d73217d7a574

neutron/tests/functional/scheduler/test_l3_agent_scheduler.py

@@ -47,7 +47,8 @@ class L3SchedulerBaseTest(test_db_base_plugin_v2.NeutronDbPluginV2TestCase):
         return agent
 
     def _create_router(self, name):
-        router = {'name': name, 'admin_state_up': True}
+        router = {'name': name, 'admin_state_up': True,
+                  'tenant_id': self.adminContext.tenant_id}
         return self.l3_plugin.create_router(
             self.adminContext, {'router': router})
 
@@ -304,7 +305,8 @@ class L3AZSchedulerBaseTest(test_db_base_plugin_v2.NeutronDbPluginV2TestCase):
 
     def _create_router(self, az_hints, ha):
         router = {'name': 'router1', 'admin_state_up': True,
-                  'availability_zone_hints': az_hints}
+                  'availability_zone_hints': az_hints,
+                  'tenant_id': self._tenant_id}
         if ha:
             router['ha'] = True
         return self.l3_plugin.create_router(