docs: def check_running(self, role, number):
      """
      Check that a certain number of instances in a role are running.
      """
      instances = self.get_instances_in_role(role, "running")
      if len(instances) != number:
        print "Expected %s instances in role %s, but was %s %s" % \
          (number, role, len(instances), instances)
        return False
      else:
        return instances