mojo: Fix python bindings tests.

mojo/tools/run_mojo_python_bindings_tests.py

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os
 import sys
 
 _script_dir = os.path.dirname(os.path.abspath(__file__))
 sys.path.insert(0, os.path.join(_script_dir, "pylib"))
 
 from mojo_python_tests_runner import MojoPythonTestRunner
 
 
 class PythonBindingsTestRunner(MojoPythonTestRunner):
 
   def add_custom_commandline_options(self, parser):
-    parser.add_argument('--build_dir', action='store',
+    parser.add_argument('--build-dir', action='store',
                         help='path to the build output directory')
 
   def apply_customization(self, args):
     if args.build_dir:
       python_build_dir = os.path.join(args.build_dir, 'python')
       if python_build_dir not in sys.path:
         sys.path.append(python_build_dir)
       python_gen_dir = os.path.join(
           args.build_dir,
           'gen', 'mojo', 'public', 'interfaces', 'bindings', 'tests')
-      print python_gen_dir
       if python_gen_dir not in sys.path:
         sys.path.append(python_gen_dir)
 
 
 def main():
   runner = PythonBindingsTestRunner(os.path.join('mojo', 'python', 'tests'))
   sys.exit(runner.run())
 
 
 if __name__ == '__main__':
   sys.exit(main())