Fix mistral CI.
Fix mistral CI.

Last update on cron triggers left this test flaky. Adding a 1 second
sleep forces it to find a next cron trigger needing to be executed

Closes-Bug: #1778736
Change-Id: Icc98d322b3db683f8f842303b9f4b555f3b1046d

openstack/mistral,openstack/mistral