Add new filter based on thresholds of metrics

Operators want to avoid scheduling more VMs on a host(HV), when the CPU usage on the HV is hot. A combination of metric weight and metrics-based filter, gives a nice way to order the HVs, while scheduling. But, it does not give a choice to exclude a HV, based on the usage. So, at present, operators resort to disable a host from scheduling to avoid further degradation of performance on the HV. At the same time, when the usage cools down, operators enable those HVs back manually. It will be useful to have a filter for the HVs based on thresholds defined for the metrics - thus automating the manual work in a programmatic way.