job_event: fix the place we print the message about unflushed events
settings: Use the boolean False for the default value of SYSTEMD_ENABLED
test_blacklist: limit the number of concurrent tasks
classic worker: make the partitions work under python3

In python 3, hash is salted and will return a different value everytime it is
invoked, therefore, it cannot be used.
ddfs: complain about missing files in ddfs push

This behaviour is preferable to silently ignoring such missing files.
Merge pull request #566 from pooya/test_blacklist

Fix a couple of cosmetic issues