QoS modeling can now running on large amount of service-instances, QoS and primitive dimensions.

1. Adding a thread pool for allocating threads, and change the termination of thread via Future object.
2. Fix an issue when the modeling time is larger than the sampling interval, then the values that awaiting
to be updated can be overwriten.

It can now run soomthly against large number of dimensions.

ref: T6
type: consolidation/testing/fix