Look at PRESUBMIT.cfg file to disable style checks

- Use ConfigParser to look for hooks to disable in PRESUBMIT.cfg file in
  the project root.
- Add sample PRESUBMIT.cfg file that disables source style hooks.
- Add README file to explain PRESUBMIT.cfg.
- Add hint that directs user to README file for disabling hooks.

TEST=Test with and without PRESUBMIT.cfg file.
     Test with and without disable flags in PRESUBMIT.cfg file
     Test without [Disable] section in PRESUBMIT.cfg file

Change-Id: Ia3a97516835f4f7f24cd35529d0e8db7afd0fbeb
Reviewed-on: http://gerrit.chromium.org/gerrit/740
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
Tested-by: Ryan Cui <rcui@chromium.org>
3 files changed
tree: 3f2433fc1570f357fbb20265c80112fec7180f0a
  2. checkpatch.pl
  3. disable_cros_style_checks/
  4. errors.py
  5. pre-upload.py