Scenarios: remove trivial wrapper methods

These methods are harmful: they break the code-reading flow, they keep
reinventing the wheel, they give the impression we don't have consistent
names for methods, etc.

"There should be one-- and preferably only one --obvious way to do it."

Change-Id: I758f003c795b656823eb81503e6e052659b257bb
diff --git a/tempest/scenario/test_minimum_basic.py b/tempest/scenario/test_minimum_basic.py
index d9c6924..f7c7434 100644
--- a/tempest/scenario/test_minimum_basic.py
+++ b/tempest/scenario/test_minimum_basic.py
@@ -62,12 +62,6 @@
             server, custom_matchers.MatchesDictExceptForKeys(
                 got_server, excluded_keys=excluded_keys))
 
-    def cinder_create(self):
-        return self.create_volume()
-
-    def cinder_list(self):
-        return self.volumes_client.list_volumes()['volumes']
-
     def cinder_show(self, volume):
         got_volume = self.volumes_client.show_volume(volume['id'])['volume']
         self.assertEqual(volume, got_volume)
@@ -115,8 +109,8 @@
 
         self.nova_show(server)
 
-        volume = self.cinder_create()
-        volumes = self.cinder_list()
+        volume = self.create_volume()
+        volumes = self.volumes_client.list_volumes()['volumes']
         self.assertIn(volume['id'], [x['id'] for x in volumes])
 
         self.cinder_show(volume)