BibSched: subdirs for bibsched logs

• Splits bibsched logs in subdirs so that do not hit the max number of file in the filesystem. Each 10k tasks a new directory is created. e.g. for task id 12040 the log will be stored in var/log/bibsched/1/bibsched_task_12040.{log,err} This happens a lot on AFS were the limit is around 20k.