Do not delete a file when CloudStorage is acting up.
Do not delete a file when CloudStorage is acting up.

The file is likely good. Use an HTTP 500 so the task scheduler retries the job
on the task's behalf. This should help a lot with the instability of the
isolateserver when GS isn't.

R=iannucci@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/17448019

git-svn-id: 8fa0a038c61565a87d0885d584517a2e12819dac@207537 0039d316-1c4b-4281-b951-d872f2087c98

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