The OrderedDict class appeared in the 'collections' module
from python 2.7 onwards, so use that in preference to our
local backport if available.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <20180116134217.8725-4-berrange@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>