Sorting of Scheduler Host Filters for Performance

Scheduler host filters range in how efficient they are when they run. Some hit the database for every host they consider. Others only operate using local data. It is best for performance if we save the more expensive filters for the end where we have eliminated as many hosts as we can using the more efficient filters.

This is to be implemented by adding an attribute to the host filter classes that gives a hint for where it should land in the sort order.

There is no user impact of this change, so no changes to documentation will be needed.