'Add Identifying Tags to all servers in the group.
This is so the Dimensions received from cfn-push-stats all include
the groupname and stack id.
Note: the group name must match what is returned from FnGetRefId'

def _tags(self):

    autoscaling_tag = [{self.TAG_KEY: 'metering.AutoScalingGroupName', self.TAG_VALUE: self.FnGetRefId()}]
    return (super(AutoScalingGroup, self)._tags() + autoscaling_tag)
