Description of problem:
Long running task watching can trigger itself under certain scenarios

Version-Release number of selected component (if applicable):
6.13+

How reproducible:
Always

Steps to Reproduce:
1. Have a long running task (paused or running for more than 2 days)
2. Wait a day

Actual results:
Long running task watching kicks in and tries to email all admin users (and users who opt in for it). It also tries to email internal admin users who don't have email set. This will fail and the task watching task will go into paused state, thus triggering the notification attempt next time the check runs. The same issue can occur if you create an admin user without email.

Expected results:
Internal admin users and users without email set are ignored (delivery to those users is not attempted at all). If the delivery does fail for some reason, the task should go into stopped-error (or warning) so that it gets out of the way and doesn't trigger itself the next time it runs.

Additional info:
Task cleanup seems to be the most reliable way to get out of this circle of broken self-reporting.