Alert hosts if tests haven't been reported for a period of time.

Hosts are contacted if tests fail when they are passing on core's TravisCI, but not when they haven't reported in some time.

There's a section on the test results page for "Registered, but no reports in >25 Revisions", and hosts may become listed there without noticing their testing infrastructure has stalled.

Let's see if we can keep that from happening as frequently.