swift pollster resources should be partitioned by tenant

[Nejc Saje]

Currently, swift doesn't use a discovery mechanism. It should have its own discovery class, which would discover swift tenants and then the pollster could receive a list of tenants as a list of resources.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/121104

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/121104
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=87afc5ada176d2062bc0cc81c248d6813941a7d4
Submitter: Jenkins
Branch: master

commit 87afc5ada176d2062bc0cc81c248d6813941a7d4
Author: Nejc Saje <email address hidden>
Date: Tue Sep 9 03:44:35 2014 -0400

    Partition swift pollster resources by tenant

    Since the latest discovery change, Swift pollsters on different
    agents only decide which who should poll. Most of the time there's
    only one endpoint, so only one agent gets to do any work.

    This patch fixes this by introducing a new TenantDiscovery, which
    enables Swift (and other in the future) pollsters to partition the
    set of keystone tenants among them and then each poll the samples
    for their assigned subset of tenants.

    Closes-Bug: #1365351
    Change-Id: Iba4a3b91d5ee978213fdd6fcf8bb62b315324a52