Ensure only one pool-manager performs periodic tasks
Ensure only one pool-manager performs periodic tasks

Before, multiple pool managers on multiple physical or
virtual machines would all run the periodic sync and
recovery tasks, by implementing leader election, we
ensure that only one pool manager, per pool, is running
these tasks.

Closes-Bug: 1445127
Change-Id: I3c062d22db188fca5f74290a44ed6cf1741951b0

ionrock/designate,cneill/designate-testing,ionrock/designate,muraliselva10/designate,muraliselva10/designate,tonyli71/designate,cneill/designate-testing,openstack/designate,ramsateesh/designate,openstack/designate,tonyli71/designate,cneill/designate-testing,tonyli71/designate,openstack/designate,muraliselva10/designate,ramsateesh/designate,grahamhayes/designate,ramsateesh/designate,grahamhayes/designate,ionrock/designate,grahamhayes/designate