Set random name in common function create_server

This is to set random name in volume.base.create_server, to avoid
random name definition everytime calling create_server.

Change-Id: I3078339806f2b3f472ce8f6010ae2364aebbf1dc
diff --git a/tempest/api/volume/test_volumes_snapshots.py b/tempest/api/volume/test_volumes_snapshots.py
index f971eca..7be31d1 100644
--- a/tempest/api/volume/test_volumes_snapshots.py
+++ b/tempest/api/volume/test_volumes_snapshots.py
@@ -45,11 +45,7 @@
     def test_snapshot_create_with_volume_in_use(self):
         # Create a snapshot when volume status is in-use
         # Create a test instance
-        server_name = data_utils.rand_name(
-            self.__class__.__name__ + '-instance')
-        server = self.create_server(
-            name=server_name,
-            wait_until='ACTIVE')
+        server = self.create_server(wait_until='ACTIVE')
         self.servers_client.attach_volume(
             server['id'], volumeId=self.volume_origin['id'],
             device='/dev/%s' % CONF.compute.volume_device_name)