Result folder logs are not separated

[Hzxin]

Description

The result folder saves the log for each bug/experiment.

Problem:
During parallel run, the log stored for each experiment is the full logs for the entire parallel run.
For benchmark like d4j, the log for the entire parallel run could go up to few GB, and each experiment in the result folder will have a copy of this log.

The disk space could be easily used up without manual cleaning.