Relax volume compare in test_minimum_basic_scenario

Similar to I50d1319b690453923b470733e94f3a11fd1cd249 for
the server that was just created, this change relaxes the
volume compare check on the updated_at field since we can
race between the time the volume was created and when comparing
to the results of GETing the volume that updated_at could have
changed.

Change-Id: Ie666b9ea0e46cf3ee22d07709e5faebafde35325
Closes-Bug: #1838202
diff --git a/tempest/scenario/test_minimum_basic.py b/tempest/scenario/test_minimum_basic.py
index cee543b..4cd860d 100644
--- a/tempest/scenario/test_minimum_basic.py
+++ b/tempest/scenario/test_minimum_basic.py
@@ -61,7 +61,11 @@
 
     def cinder_show(self, volume):
         got_volume = self.volumes_client.show_volume(volume['id'])['volume']
-        self.assertEqual(volume, got_volume)
+        # Exclude updated_at because of bug 1838202.
+        excluded_keys = ['updated_at']
+        self.assertThat(
+            volume, custom_matchers.MatchesDictExceptForKeys(
+                got_volume, excluded_keys=excluded_keys))
 
     def nova_reboot(self, server):
         self.servers_client.reboot_server(server['id'], type='SOFT')