Rbd backend doesn't support disk IO qos

[StephenSun]

Honor https://wiki.openstack.org/wiki/InstanceResourceQuota#IO_limits by propagating
the extra_specs also in the RBD sub-class.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/143939

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/143939
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=fdb7b030abbff85d19581c3f2b0ba68683fd8d6f
Submitter: Jenkins
Branch: master

commit fdb7b030abbff85d19581c3f2b0ba68683fd8d6f
Author: StephenSun <email address hidden>
Date: Thu Dec 25 12:04:03 2014 +0800

    libvirt: fix disk I/O QOS support with RBD

    The disk I/O QOS settings were set in the libvirt_info
    method of the Image class. While this is fine for most
    subclasses, the Rbd subclass overrides this method and
    so was loosing the QOS settings. Move the setting of
    QOS parameters into a separate method so it can be
    called in all places that need it. For added fun the
    commit 86e6f34 which added QOS settings originally never
    added any unit tests to cover its operation.

    Co-authored: Daniel P. Berrange <email address hidden>
    Fixes bug #1405367
    Change-Id: Ibb3a4dff8996c29ef921be7c56648a442bbb89a2

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/kilo
Review: https://review.openstack.org/231925

[OpenStack Infra (hudson-openstack)]

Change abandoned by Francois Deppierraz (<email address hidden>) on branch: stable/kilo
Review: https://review.openstack.org/231925
Reason: Ok, let's abandon this backport.

[Tony Breeds (o-tony)]

Removed the kilo-backport-potential as the backport isn't appropriate for a "Phase II" Stable branch