Improve an error message to be more explicit.

Make an error message about a bad URL include the URL in question. Also clean
up an exception definition oddity flagged by the linter.

BUG=None
TEST=Saw improved error message after the change, image_to_live.sh.

Change-Id: Ie7df9126c174ceedf2ed296fa22ea4c03d75b1cc
Reviewed-on: https://chromium-review.googlesource.com/167734
Tested-by: Don Garrett <[email protected]>
Reviewed-by: Chris Sosa <[email protected]>
Commit-Queue: Don Garrett <[email protected]>
1 file changed