Remove unused imports and fix some other linter errors.

unittests/autoroll_test.py

 #!/usr/bin/env python
 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import json
 import os
 import subprocess
 import sys
 import unittest
 
 import repo_test_util
 
-from recipe_engine import package
-
 
 class TestAutoroll(repo_test_util.RepoTest):
   def run_roll(self, repo, *args):
     """Runs the autoroll command and returns JSON.
     Does not commit the resulting roll.
     """
     with repo_test_util.in_directory(repo['root']), \
         repo_test_util.temporary_file() as tempfile_path:
       subprocess.check_output([
           sys.executable, self._recipe_tool,
@@ skipping 479 matching lines @@
         '--project=c',
         '--project=d',
     )
     self.assertFalse(roll_result['success'])
     self.assertFalse(bool(roll_result['roll_details']))
     self.assertFalse(bool(roll_result['rejected_candidates_details']))
 
 
 if __name__ == '__main__':
   sys.exit(unittest.main())