We have trouble rolling dep of the grpc library. It looks like buildbots
use git_cache to download cache of the library from cloud storage, but
the way it picks up the latest cache is to do a string sort on the
filenames then pick the last one. This won't work if the filenames have
digit carrying, say you have both 9999.zip and 10000.zip, then 9999.zip
will get picked up.

This CL fixes this by implementing a new filename sorting logic that
extracts the numeral part of the filename and sort on it.

Bug: 927154
Change-Id: I68fce3fe67e55ce5092e7e9dc1dca606b427fe87
Reviewed-on: https://chromium-review.googlesource.com/c/1448954
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>