test: format_exc in 3rd assert* method argument is pointless.

Just call cli.manage directly to get produced exception, as it's what this
part of the test is really about.

caucase/test.py

@@ -2261,16 +2261,20 @@ class CaucaseTest(unittest.TestCase):
       stdout.getvalue().splitlines(),
     )
 
-    self.assertEqual(
-      self._restoreServer(
+    try:
+      caucase.http.manage(
+        argv=(
+          '--db', self._server_db,
+          '--restore-backup',
           backup_path,
           user2_key_path,
           user2_new_csr_path,
           user2_new_key_path,
         ),
-      0,
-      traceback.format_exc(),
       )
+    except SystemExit as e:
+      if e.code:
+        raise
 
     after_restore = list(SQLite3Storage(
       self._server_db,