swarming: enable get_callbacks cron
swarming: enable get_callbacks cron

BUG=940013

Change-Id: I55a03b996065f188e8aba04e8aa7866039ac2e3c
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1512797
Commit-Queue: Aviv Keshet <178e8ae417efbe404feca7ab4cb8f0ba8c109369@chromium.org>
Reviewed-by: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

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