python: Convert dict iterators.

In Python 2, dict.items(), dict.keys(), and dict.values() returned a
list.  dict.iteritems(), dict.iterkeys(), and dict.itervalues() returned
an iterator.

As of Python 3, dict.iteritems(), dict.itervalues(), and dict.iterkeys()
are gone.  items(), keys(), and values() now return an iterator.

In the case where we want an iterator, we now use the six.iter*()
helpers.  If we want a list, we explicitly create a list from the
iterator.

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>

python/build/nroff.py

@@ -89,7 +89,7 @@ def inline_xml_to_nroff(node, font, to_upper=False, newline='\n'):
                 s += node.attributes['db'].nodeValue
             else:
                 raise error.Error("'ref' lacks required attributes: %s"
-                                  % node.attributes.keys())
+                                  % list(node.attributes.keys()))
             return s + font
         elif node.tagName in ['var', 'dfn', 'i']:
             s = r'\fI'