1124570 - Adds two-queue implementation for reserved resources

https://bugzilla.redhat.com/show_bug.cgi?id=1124570

This BZ implements this [design and TODO list](https://fedorahosted.org/pulp/wiki/TwoQueueReservedResourceDesign). Refer to that doc for more info on what is contained in this PR.
I think it should queue to release the resource in all possible cases because that worker has already had the reserved_resource made for it on line 64. As its written now, until the record created on line 64 is removed, this worker is unusable because it's considered reserved by the resource manager. Recovering from that situation happens if the worker restarts or the work is explicitly cancelled.

Regarding the use of worker.queue_name, that would have resulted in a bug that only shows itself after the worker restarts without httpd restarting. Good catch!