fix accessing product info from configuration
    
    Previously, the `products` dict mapped product names in Fedora to their
    Bugzilla counter parts. Now that all information pertaining products is
    in this dictionary, the Bugzilla product name (if differing) is in the
    bz_product_name sub-key.
    
    Rename some variables to make their purpose a little more obvious, and
    not use `product` for two different things (names and the informational
    dictionary stored in the product cache).
    
    fixes: #32
    
    Signed-off-by: Nils Philippsen <nils@redhat.com>