Refactoring: Move options from cli.py to cli_opts.py

The cli.py module exceeded our max-module-lines limit and needs to be
split.

This pulls out all command line option definitions into a separate module.

It uses cli_opts instead of cli.opts since importing a module below
your own path causes problems if you want to re-export everything
from the lower module (which we want in this case).

Signed-off-by: Niklas Hambuechen <niklash@google.com>