Log instances to test (refs #20760).

tester.py

@@ -169,6 +169,7 @@ class Tester():
                     max_instances = 2
                 if len(ms_users) > max_instances:
                     ms_users = ms_users[:max_instances]
+            log('Instances that will be tested: %s.' % ', '.join(ms_users))
             # Clone testing suite
             ms_path = os.path.join(path, 'ms-testing-suite')
             if os.path.exists(ms_path):