Disable periodic tasks during integration tests

While debugging various test failures, I was confused several times by
weirdness caused by periodic tasks running during the tests.

It doesn't seem to make much sense to allow this to happen, even if it
doesn't appear to affect the tests.

Change-Id: I75d34b5ee2bf76b64ae8ba108d9c78b741ce4574
Merge "Disable periodic tasks during integration tests"