Calculates a score of a node depending on the result of executors.

The score for the node is calculated by multiplying scale and executor score. See followings for details.

score of node = (Scale for Scores) * (executor score)
scale = (Scale Adjustment for Older Builds) * (# of builds from the last build)
executor score = (idle executor score) + (busy executor score)
idle executor score = (Score for Idle Executor) * (# of builds that the node can accept now)
busy executor score = (Score for Busy Executor) * (# of builds that are running on the node)