Refactoring: Deprecate optparse in push and merge scripts.

- Deprecate optparse with argparse
- The tests include now options parsing by default: each test specifies the command-line args to parse rather than the options directly

This CL is split off from https://codereview.chromium.org/173983002/

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/179743003

git-svn-id: https://v8.googlecode.com/svn/trunk@19550 ce2b1a6d-e550-0410-aec6-3dcde31c8c00