The replicator already supports --devices and --partitions to restrict
its operation to a subset of devices and partitions. However,
operators don't always want to replicate a partition in all policies
since different policies (usually) have different rings.
For example, if I know that policy 0's partition 1234 is has no
replicas on primary nodes due to over-aggressive rebalancing, I really
want to find a node where the partition isa and make the replicator
push it onto the primaries. However, if I haven't been messing with
policy 1's ring, its partition 1234 is fine. With the existing
replicator args, I get both or neither; this commit lets me get just
the useful one.
Change-Id: Ib1d58fdd228a6ee7865321e65d7c04a891fa5c49
3ac43e8299