Revert commit with bug and prevent cpu burning

My previous commit that enables Task class to be added from configuration causes master to import from user code. This results in worker importing the users code at the time of masters initialization. This is bad if user is making a deploy and restarting the workers in hope that they will start with the new code.

If a worker can't start because of an error, master frantically tries to restart it. This increases the cpu load on server. Added a sleep to prevent that.