Add a get_rank() method to OptionValueContainer.
Review Request #2431 - Created July 1, 2015 and submitted
It returns the rank of the value at the specified key. This will be useful in another change I'm working on that reworks the option help system.
Unit tests pass locally. Full CI passed here: https://travis-ci.org/pantsbuild/pants/builds/69067709.
Status: Closed (submitted)
Submitted as 11c9ae750122dc6b0a7ca371919eaf3adafdff6f.