Replicas cohosted on a rack shouldn't keep triggering Balancer

Currently, Balancer has a shortcut check for cohosted replicas of the same region/host/rack and will keep triggering balancer if it is non-zero.

With the trending of kube and cloud solution for HBase, operators don't have full control of the topology or are not even aware of the topology. There are cases that it is not possible to satisfy or requires sacrificing other constraints such as region count balancing on RS. We want to keep there per RS/host check for availability of regions, especially for meta region. We haven't heard problem with rack so far. The cost functions will still be considered during balancing.