Use parenthesis instead of backslashes in tempest folder

Use parenthesis instead of backslashes in tempest folder

TrivialFix
Change-Id: I6c2ea07b0bfc5852b28e44989406cc10eb912e33
diff --git a/manila_tempest_tests/tests/scenario/manager.py b/manila_tempest_tests/tests/scenario/manager.py
index 64c5e8a..5cd4253 100644
--- a/manila_tempest_tests/tests/scenario/manager.py
+++ b/manila_tempest_tests/tests/scenario/manager.py
@@ -961,8 +961,8 @@
                                                  nic)
         source_host = source.ssh_client.host
         if should_succeed:
-            msg = "Timed out waiting for %s to become reachable from %s" \
-                % (dest, source_host)
+            msg = ("Timed out waiting for %s to become reachable from %s"
+                   % (dest, source_host))
         else:
             msg = "%s is reachable from %s" % (dest, source_host)
         self.assertTrue(result, msg)