Comment 0 for bug 1685787

I create a continus audit used vm_workload_consolidation strategy, and find some problems.
1.First audit, self._compute_model is none, and it will build self._compute_model use watcher_cluster_data_model_collectors. The next audit, the self._compute_model is still none, which make me confused.
2.Once a compute node is set disabled, it will never be removed from self._compute_model, because scoped_model only return enable node. There may be some problem with ServerConsolidation Strategy. If all the enabled compute nodes are overloaded, but the instance can't migrate to disabled nodes.