Make symupload exit with an error code when command-line parsing fails.

This should address the issue where some Chrome builds were failing to
upload symbols due to a bad command-line flag, but there was no
indication of a problem, and no build failure, because symupload was
exiting with a success code.

BUG=1091387
R=nbilling@google.com, wuwang@google.com

Change-Id: I0d7f1a6d689ca5fd37be3abad4c5ebc97f108e50
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/2231574
Reviewed-by: Nelson Billing <nbilling@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>