Mark FakeLatencyTracker as flaky

DeviceConfig callbacks often block indef and cause test module timeouts.

Add a test timeout for this class and mark them as flaky to take out of
presubmit.

TODO: 275746222 - don't rely on these callbacks, and instead mock/fake
the config, since it isn't related to what we are testing.

Bug: 287361279
Bug: 289392471
Merged-In: I603ebe0ceac23335248a8cdb299d52829b55536a
Change-Id: I603ebe0ceac23335248a8cdb299d52829b55536a