Use base.create_test_server_group to create server group

In test_create_server_with_scheduler_hint_group, the multi lines
to create test server group can be replaced by a call to base.
create_test_server_group to make code clean.

Change-Id: If6517c302994657aa82777794164e07a9bc0546a
diff --git a/tempest/api/compute/servers/test_create_server.py b/tempest/api/compute/servers/test_create_server.py
index 78f0db4..4fc54c8 100644
--- a/tempest/api/compute/servers/test_create_server.py
+++ b/tempest/api/compute/servers/test_create_server.py
@@ -144,14 +144,7 @@
     @test.idempotent_id('ed20d3fb-9d1f-4329-b160-543fbd5d9811')
     def test_create_server_with_scheduler_hint_group(self):
         # Create a server with the scheduler hint "group".
-        name = data_utils.rand_name('server_group')
-        policies = ['affinity']
-        body = self.server_groups_client.create_server_group(
-            name=name, policies=policies)['server_group']
-        group_id = body['id']
-        self.addCleanup(self.server_groups_client.delete_server_group,
-                        group_id)
-
+        group_id = self.create_test_server_group()['id']
         hints = {'group': group_id}
         server = self.create_test_server(scheduler_hints=hints,
                                          wait_until='ACTIVE')