1142881 - Fixes SELinux policy to allow sqlite generation to occur

https://bugzilla.redhat.com/show_bug.cgi?id=1142881

This PR does 3 things:
* allows for tmp file writing by celery_t processes, and call seetsched on process (sqlite generation support)
* makes auth_read_passwd available on both fedoras and rhel7. I believe this is needed for fedora which was never tested, but has been now.
* adds some documentation to start organizing the pulp-celery SELinux policy

This was tested on EL6, EL7, FC19, and FC20 with Enforcing enabled. I tested a create->sync->publish->delete of a repo, and then a consumer register->bind->update->unbind->unregister on each.