Modules: added worker_affinity parameter for js_periodic directive.

Modules: added worker_affinity parameter for js_periodic directive.

worker_affinity specifies on what set of workers the js_periodic handler
should be executed. By default the js_handler is executed only on worker 0.
The parameter accepts a binary mask or "all" to specify all workers.

example.conf:
worker_processes 4;

...
    location @periodics {
        # to be run at 1 minute intervals in worker 0
        js_periodic main.handler interval=60s;

        # to be run at 1 minute intervals in all the workers
        js_periodic main.handler interval=60s worker_affinity=all;

        # to be run at 1 minute intervals in workers 1 and 3
        js_periodic main.handler interval=60s worker_affinity=0101;
    }