Fix UnboundLocalError in net.py when URL fetch always times out.
Fix UnboundLocalError in net.py when URL fetch always times out.

R=nodir@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1076323006

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py