Daemonization support for dynflow executor

One can use `bin/dynflow-executor` from the Foreman rails root
to run dynflow executor. Supported commands:

    start - start executor on background, waits till the executor is ready
    stop - stop the executor
    restart - restarts the executor
    run - run the executor in foreground
Merge pull request #14 from iNecas/daemonize

Daemonization support for dynflow executor