Enhances get_meters to return unique meters

[OpenStack Infra]

https://review.openstack.org/259626
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/ceilometer" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit 52f48485eeed50dfa4705fc73e278214eb9a7f00
Author: Rohit Jaiswal <email address hidden>
Date: Fri Dec 18 12:56:59 2015 -0800

    Enhances get_meters to return unique meters

    Enhances get_meters in the storage layer
    and API to accept a unique flag and return
    back a list of unique meters for clients like
    Horizon to consume.

    DocImpact
    Change-Id: Ifdcb907df867ae650eae733bc7b635a283939064
    Closes-Bug: 1506959

[gordon chung (chungg)]

no one worked on ceilometer legacy storage for over a year. use gnocchi or something else