Drop all the calls to .keys() when iterating on the keys of a dict

Drop all the calls to .keys() when iterating on the keys of a dict

When browsing the keys of a dictionary, you can use the ``.keys()`` method but
that is in fact only really useful if you want to store the list of keys first
and act on them (like sorting them or so).
If you just want to iterate through all the keys, no matter the order, then it
is much much faster to just do: ``for key in dict``

Some stats about this can be found there:
http://blog.pingoured.fr/index.php?post/2012/03/12/Python-notes-to-self

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>
Reviewed-by: Simo Sorce <simo@redhat.com>