rust_uprev: support -rN ebuilds

rust_uprev currently doesn't fully support ebuilds with -r123 after
Rust's version number. This CL aims to help us support those better.

BUG=chromium:1136579, chromium:1112551
TEST=Ran the script

Change-Id: I22a09ec3f5d074be547783e4cb9b702d4aad0bd2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2462925
Reviewed-by: Tiancong Wang <tcwang@google.com>
Tested-by: George Burgess <gbiv@chromium.org>
2 files changed