Remove _create_router in scenario.manager

_create_router is used only once in scenario.manager, so this is to:
1. remove _create_router
2. move the logic of creating router to _get_router
3. pass external_gateway_info argument to client.create_router
   instead of using client.update_router
4. use self.__class__.__name__ as prefix of random router name
5. remove self.assertEqual(router['name'], name), and add this
   check in api test test_create_show_list_update_delete_router.

Change-Id: I5aa5a42aaa1ebd654b7e979e3807d3edbf2efa9e

tempest/api/network/test_routers.py

@@ -65,9 +65,12 @@ class RoutersTest(base.BaseNetworkTest):
                           'The public_network_id option must be specified.')
     def test_create_show_list_update_delete_router(self):
         # Create a router
+        name = data_utils.rand_name(self.__class__.__name__ + '-router')
         router = self._create_router(
+            name=name,
             admin_state_up=False,
             external_network_id=CONF.network.public_network_id)
+        self.assertEqual(router['name'], name)
         self.assertEqual(router['admin_state_up'], False)
         self.assertEqual(
             router['external_gateway_info']['network_id'],

tempest/scenario/manager.py

@@ -1124,31 +1124,18 @@ class NetworkScenarioTest(ScenarioTest):
             body = client.show_router(router_id)
             return body['router']
         elif network_id:
-            router = self._create_router(client, tenant_id)
-            kwargs = {'external_gateway_info': dict(network_id=network_id)}
-            router = client.update_router(router['id'], **kwargs)['router']
+            router = client.create_router(
+                name=data_utils.rand_name(self.__class__.__name__ + '-router'),
+                admin_state_up=True,
+                tenant_id=tenant_id,
+                external_gateway_info=dict(network_id=network_id))['router']
+            self.addCleanup(test_utils.call_and_ignore_notfound_exc,
+                            client.delete_router, router['id'])
             return router
         else:
             raise Exception("Neither of 'public_router_id' or "
                             "'public_network_id' has been defined.")
 
-    def _create_router(self, client=None, tenant_id=None,
-                       namestart='router-smoke'):
-        if not client:
-            client = self.routers_client
-        if not tenant_id:
-            tenant_id = client.tenant_id
-        name = data_utils.rand_name(namestart)
-        result = client.create_router(name=name,
-                                      admin_state_up=True,
-                                      tenant_id=tenant_id)
-        router = result['router']
-        self.assertEqual(router['name'], name)
-        self.addCleanup(test_utils.call_and_ignore_notfound_exc,
-                        client.delete_router,
-                        router['id'])
-        return router
-
     def create_networks(self, networks_client=None,
                         routers_client=None, subnets_client=None,
                         tenant_id=None, dns_nameservers=None,