Fix the exception message in tempest plugin

Follow up to commit 733ff3fff71f8781414befe40aaca3c6492cda6b

Change-Id: I3498268c6dd7626c1e99ded9fdfb287b4197c999
diff --git a/ironic_tempest_plugin/common/waiters.py b/ironic_tempest_plugin/common/waiters.py
index 7cfc12e..b706ac0 100644
--- a/ironic_tempest_plugin/common/waiters.py
+++ b/ironic_tempest_plugin/common/waiters.py
@@ -106,7 +106,7 @@
 
     if not test_utils.call_until_true(is_some_node_associated, timeout,
                                       interval):
-        msg = ('Timed out waiting to get Ironic node by instance ID '
-               '%(instance_id)s within the required time (%(timeout)s s).'
-               % {'instance_id': instance_uuid, 'timeout': timeout})
+        msg = ('Timed out waiting to get Ironic node by instance UUID '
+               '%(instance_uuid)s within the required time (%(timeout)s s).'
+               % {'instance_uuid': instance_uuid, 'timeout': timeout})
         raise lib_exc.TimeoutException(msg)