Fix references to api proxy exceptions.
Fix references to api proxy exceptions.

BUG=
R=maruel@chromium.org

Review URL: https://codereview.appspot.com/14500043

luci/luci-py,pombreda/swarming,luci/luci-py,madecoste/swarming,pombreda/swarming,luci/luci-py,pombreda/swarming,luci/luci-py,madecoste/swarming,madecoste/swarming,madecoste/swarming,pombreda/swarming