Increase the number of retries for deleting the temporary directory.
Increase the number of retries for deleting the temporary directory.

We're seeing frequent timeouts of certain Telemetry based tests on the
Windows GPU bots. Let's increase the number of retries for cleaning up
the temporary directory, implicitly doubling the timeout from 6 to 12
seconds, to see whether this changes the behavior.

BUG=348764
R=vadimsh@chromium.org

Review URL: https://codereview.appspot.com/70980043

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