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 wouldn't suggest changing this pattern for this PR, but I would say that I prefer the more traditional decorator approach to mocking, as it allows me to read in one "screen" of text both the test and it's mocks without having to scroll to the setUp() to see what the mocks are doing.

That said, I can appreciate the reduction in code repetition that results from doing it this way.