Config by hostname

this enables by-hostname configuration for resque-pool.
environment variables can still be used as usual.

example
<pre>
general_job1: 1
general_job2: 1

staging:
    staging_worker: 1

workers-production-1:
    can_only_be_run_once: 1
    generic_worker: 5

workers-production-2:
    generic_worker: 10
</pre>