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

def ex_list_image_versions(self, sku):

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