'List node image offers from a publisher.
:param publisher: The complete resource path to a publisher
(as returned by `ex_list_publishers`)
:type publisher: ``str``
:return: A list of tuples in the form
("offer id", "offer name")
:rtype: ``list``'

def ex_list_offers(self, publisher):

    action = ('%s/artifacttypes/vmimage/offers' % publisher)
    r = self.connection.request(action, params={'api-version': '2015-06-15'})
    return [(p['id'], p['name']) for p in r.object]
