fix bug in num_instances_per_host_consrtaint, need more tests.
added solver_scheduler_host_manager that contains new features of solver scheduler while compatible with the base host_manager, updated solver_scheduler to avoid previous changes in filter_scheduler so the original filter_scheduler in official openstack release will not be affected.
added network affinity (host/rack/aggregate) related costs and constraints.
fix bugs in solver host manager.
Change the method to get host instances info, this way requires less db queries.
get networks in host states from instance info, avoid calling neutron.
remove the old host manager, let new host manager inherit from it.
remove the old filter scheduler, let new solver scheduler inherit from it.
fix bugs in new host manager.