Adding dev-notes for try-catch block in periodic task
Adding dev-notes for try-catch block in periodic task

Not removing existing try-catch block for sync_bay_status and other
periodic tasks. Rather leaving a note with the pointers and explanation
for developers to add new periodic task.

Change-Id: I2560d3961c19d73ab78a8e9812d69742c6bd2117
Closes-Bug:1496094

dimtruck/magnum,openstack/magnum,jay-lau/magnum,dimtruck/magnum,ArchiFleKs/magnum,openstack/magnum,ArchiFleKs/magnum