Some bots run roll-dep.py and fail while generating the commit message
with the following error:

  src/ios/third_party/material_components_ios/src: Rolling from 54fd1dac39 to 5aaf54801f
  fatal: ambiguous argument '54fd1dac3..5aaf54801': unknown revision or path not in the working tree.
  Use '--' to separate paths from revisions, like this:
  'git <command> [<revision>...] -- [<file>...]'

As "Rolling from 54fd1dac39 to 5aaf54801f" is printed, this mean that
the bot was able to resolve both HEAD and roll_to before invoking this
function, thus the corresponding hashes exists in the repository.

It is unlikely that shortening the hash to just the first nine chars
results in a collision, but there is no reason to use a short hash
when invoking git anyway, so use a separate variable to construct the
header of the commit with short hashes while invoking git with the
full hashes.

Also pass '--' after all the parameters to force git to interpret the
hash range as a range and not as a path.

This is a speculative fix.

Change-Id: Iaa2888610dcf8e20f9edc115a719791d573b83ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2031104Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>