Solved one issue with the worker and some code refactoring 

Solved issue when testing if worker is alive, this lead to bad worker registering and unregistering and so bad worker pool management.

Added getters and setters for hostname, pid, 
Added getter for id which is now constructed from pid, hostname and queues.

When a worker is launched, we update pid when we call the ```php startup() ``` method so that the worker gets the right pid after being forked.