MDL-69419 core: Task reset tests cannot use random test times

MDL-69419 core: Task reset tests cannot use random test times

If a scheduled task which uses a 'R' field is picked, then the reset of
updated task times will not necessarily be correctly determined as the
randomisation is picked during reset.

This can lead to some random test failures.

Actively specifying a test which does not make use of the 'R' random
field time addresses this issue.