Add error message to presubmit failure

Add error message to pre-upload script in the case where the remote branch does
not fit the standard '<remote>/<branch name>' format.

Previously the presubmit checks would error without printing the
relevant branch name.

BUG=None
TEST=repo upload .
Change-Id: I82545f3661b4f0403da71da73027b4b7e115d62a
Reviewed-on: https://chromium-review.googlesource.com/1179113
Commit-Ready: Josh Pratt <jopra@chromium.org>
Tested-by: Josh Pratt <jopra@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed