python: Better iterate over dictionaries

python: Better iterate over dictionaries

In Python 2, dictionaries have 2 sets of methods to iterate over their
keys and values: keys()/values()/items() and iterkeys()/itervalues()/iteritems().

The former return lists while the latter return iterators.

Python 3 dropped the method which return lists, and renamed the methods
returning iterators to keys()/values()/items().

Using those names makes the scripts compatible with both Python 2 and 3.

Signed-off-by: Mathieu Bridon <bochecha@daitauha.fr>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>