reschedule (#6860)

* reschedule

* add tests

* Apply suggestions from code review

Co-authored-by: Dan Forbes <[email protected]>

* add test for reschedule named perodic

* update test

* handle the case when reschedule does not change time

Co-authored-by: Dan Forbes <[email protected]>
Co-authored-by: Shawn Tabrizi <[email protected]>