Custom RGW Bucket to RADOS Pool mapping

Sometimes, it is useful to be able to map RGW bucket to specific RADOS pool, for example to apply different data distribution or replication rules depending on the bucket.
The current (0.60) behavior of RGW is just to choose a random RADOS pool among the ones you assigned to RGW (using radosgw-admin pool add). The attached patch, instead of choosing randomly, will try to match the bucket name to the RADOS poolname. If you create a bucket named XXXX.YYYY , it will scan through all the RADOS pool you've assigned to RGW and try to find one named .rgw.XXXX and if it doesn't find one, it will fallback to .rgw.buckets (the default one)