Skarmark 999129

https://bugzilla.redhat.com/show_bug.cgi?id=999129

Related PR in pulp - https://github.com/pulp/pulp/pull/648

This also resolves https://bugzilla.redhat.com/show_bug.cgi?id=1014787

Here is a refresher on the way server side content apis work if you are new to the upload area like me ;) 
http://pulp-dev-guide.readthedocs.org/en/latest/integration/rest-api/content/upload.html

There are were a couple of issues causing a race condition mentioned in bug 999129 - 

1. Upload_manager initialization (which is done when loading iso and rpm upload cli sections) loads current tracker files without considering that they might be getting processed and deleted at the same time. 
2. iso and rpm uploads use the same upload_working_dir which also contributes to the race condition and causes bug 1014787.

These 2 PRs resolve this by -
1. Removing tracker files loading at the time of initializing upload_manager. We really don't need them unless executing list or resume of paused uploads. 
2. When loading these files, it catches and ignores IOError as it can be getting processed and deleted at the same time. So essentially it is a  best effort listing of remaining uploads.
3. rpm and iso uploads use different subdirectories for upload tracker files.