Continuation of I0b540e54dbabd26901a7530035a38583bb521fda
* delete scheduler.simple
* modify scheduler.multi instead of delete to continue supporting
I753e87fc8979fd0b62529974f00cf11fa55b3d63
* update scheduler.multi docstring
* scheduler.rpcapi bumped to 2.3
* change default scheduler to scheduler.filter_scheduler
DocImpact
part of bp delete-nova-volume
Change-Id: Ie9d9b46742b2d92cd1e9ffe982ef658907a1d411