aggregator transformer needs different behavior for cumulative meters

[Nejc Saje]

Currently, it just sums up the volumes of all aggregated samples.

In the case of cumulative meters, it should just take the volume of the last sample received.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/108315

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/108315
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=454eba9e9e4db8c32657feb86cf28608ff0c3be1
Submitter: Jenkins
Branch: master

commit 454eba9e9e4db8c32657feb86cf28608ff0c3be1
Author: Nejc Saje <email address hidden>
Date: Mon Jul 21 10:25:25 2014 +0200

    Add cumulative and gauge to aggregator transformer

    Currently, the aggregator transformer just sums up the volumes of all
    aggregated samples.

    This patch improves it so it returns just the latest volume for cumulative
    meters and the average of volumes for gauge meters.

    DocImpact: Aggregator transformer now works for gauge and cumulative as well
    Change-Id: I172a7298dc063ff36b2a209df25d6650debb5a14
    Closes-bug: #1342668