Fix and cleanup Mojo and Mandoline python scripts.

mandoline/tools/android_run_mandoline.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 argparse
 import logging
 import os
 import sys
 
@@ skipping 10 matching lines @@
   logging.basicConfig()
 
   parser = argparse.ArgumentParser(usage=USAGE)
 
   debug_group = parser.add_mutually_exclusive_group()
   debug_group.add_argument('--debug', help='Debug build (default)',
                            default=True, action='store_true')
   debug_group.add_argument('--release', help='Release build', default=False,
                            dest='debug', action='store_false')
   parser.add_argument('--target-cpu', help='CPU architecture to run for.',
-                      choices=['x64', 'x86', 'arm'])
+                      choices=['x64', 'x86', 'arm'], default='arm')
   parser.add_argument('--target-device', help='Device to run on.')
   launcher_args, args = parser.parse_known_args()
 
   config = Config(target_os=Config.OS_ANDROID,
                   target_cpu=launcher_args.target_cpu,
                   is_debug=launcher_args.debug,
                   apk_name="Mandoline.apk")
   paths = Paths(config)
-  shell = AndroidShell(paths.target_mojo_shell_path, paths.build_dir,
-                       paths.adb_path, launcher_args.target_device,
+  shell = AndroidShell(paths.mojo_runner, paths.build_dir, paths.adb_path,
+                       launcher_args.target_device,
                        target_package='org.chromium.mandoline')
 
   extra_shell_args = shell.PrepareShellRun()
   args.extend(extra_shell_args)
 
   shell.CleanLogs()
   p = shell.ShowLogs()
   shell.StartShell(args, sys.stdout, p.terminate)
   return 0
 
 
 if __name__ == "__main__":
   sys.exit(main())