Allow option to disable relocation of commands on failover

Provide option to disable rescheduling of commands to other nodes when topologies have changed. Packet-ng should handle this more gracefully, but it would still be helpful to avoid non-idempotent operations from being retried.

Currently we don't have the facilities to inspect (in 2.3.x) which operations should be retried and which shouldn't be, but we should add this as an extensible option in any event.