Update meters definition reference
Update meters definition reference

Meters definiton confiuration has change since[1]. So the related
reference has to be up-to-date.

[1]Iad15476cabd1f35f13322a0903f4ff0abf9a0160

Change-Id: I9f48d28fea70c155316cd3eecf465130114a5f4c

openstack/ceilometer,openstack/ceilometer