Replace deprecated scheduler filter module name
Replace deprecated scheduler filter module name

manila.scheduler.filter_scheduler.*Scheduler was deprecated long ago[1]
in favor of new manila.scheduler.drivers.filter.*Scheduler.

[1] 3ffb4979f328259793079a5ece6f3b79e23f5187

Change-Id: I40349cbe106f688a67043a73f8563f87f069831b

openstack/manila,openstack/manila