RPM Support

Originally reported by a user here: https://www.redhat.com/archives/pulp-list/2016-March/msg00041.html

In 2.6 (and earlier), at the completion of each rpm download, the file would be moved from its temporary location to a permanent location. That means for any given sync, you would never have more files in that temporary location than you did concurrent downloads. Using the default setting of 5 concurrent downloads, that's a maximum of 5 rpms. No problem so far.

This change turned the "move" into a "copy":

https://github.com/pulp/pulp_rpm/commit/de1895ede2f24731dcf6f52321beaee6b71c15a4

Now all of the rpm files pile up, and they don't get removed until the end of the task. On quick glance, it appears that 2.8 suffers the same problem, although the code has been refactored.