Fix fail test_iscsi_volume

In _volume_clean_up method to get volume used volumes_client
with get_volume while show_volume should be used instead

Closes-bug: #1451759

Change-Id: Ic3413b36fc2b45b0e09c5b02d15e1f71b2585cc7
diff --git a/tempest/api/compute/admin/test_live_migration.py b/tempest/api/compute/admin/test_live_migration.py
index 8a92326..0b0f4d5 100644
--- a/tempest/api/compute/admin/test_live_migration.py
+++ b/tempest/api/compute/admin/test_live_migration.py
@@ -78,7 +78,7 @@
             return server_id
 
     def _volume_clean_up(self, server_id, volume_id):
-        body = self.volumes_client.get_volume(volume_id)
+        body = self.volumes_client.show_volume(volume_id)
         if body['status'] == 'in-use':
             self.servers_client.detach_volume(server_id, volume_id)
             self.volumes_client.wait_for_volume_status(volume_id, 'available')