Rework nuke_buckets

Nuke all buckets on the master, sync, and then
nuke any remaining buckets on non-master regions.

Signed-off-by: Joe Buck <jbbuck@gmail.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Moving region_sync to utils

Since other classes need to do syncs,
let's move it to the utils file.

Signed-off-by: Joe Buck <jbbuck@gmail.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>