This option is useful in large deployments.
Our scheduler strategy is to "pack", however we are not interested in this
strategy per individual compute node but per sets of them. One of the
advantages is that when a user creates consecutive instances in the same
AVZ it's unlikely that they will be
[resending to include the operators list]
The host_subset_size configuration option was added to the scheduler to help
eliminate race conditions when two requests for a similar VM would be processed
close together, since the scheduler’s algorithm would select the same host in
both cases,
