* Add parl monitor.

* Add clustermonitor.py

* Fix thread safety bug.

* Fix js bugs.

* Fix End of Files.

* fix cluster_test bug

* yapf error

* fix bugs in tests/job_center_test.py

* fix bugs in tests/job_center_test.py

* add test_cluster_monitor.py

* add worker.exit in test_cluster_monitor.py