chore: fix python lint warnings (#14638)

* chore: fix lint warnings

* chore: another try at python import errors

Looks like the problem is that dbus_mock.py is running as
a script but living in the `lib/` directory where it's part of a
module. Moving it up into the `script/` directory seems to
solve the issue.

script/pump.py

@@ -62,12 +62,12 @@ GRAMMAR:
        EXPRESSION has Python syntax.
 """
 
-__author__ = 'wan@google.com (Zhanyong Wan)'
-
 import os
 import re
 import sys
 
+__author__ = 'wan@google.com (Zhanyong Wan)'
+
 
 TOKEN_TABLE = [
     (re.compile(r'\$var\s+'), '$var'),