os-used-limits API extension should optionally include the reserved count

[Eoghan Glynn]

By omitting the reserved count from the total<Resource>Used elements in the response, the os-used-limits API extension prevents the caller from gaining the most accurate picture of the actual headroom.

For example, if the current instances quota is 10, the in_use count is 9 and an instance creation is in-flight, then the values for maxTotalInstances and totalInstanceUsed will imply that there is headroom to create a further resource. In fact this will not be the case, as the single reserved instance will prevent a new instance being spun up.

We should support a query param to control whether the reserved count is included:

  GET /v2/<TENANT_ID>/limits => do not include reserved count

  GET /v2/<TENANT_ID>/limits?reserved=0 => do not include reserved count

  GET /v2/<TENANT_ID>/limits?reserved=1 => include reserved count in the total<Resource>Used values

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/17805

[Eoghan Glynn (eglynn)]

This fix, or equivalent, is required to fully address this Horizon bug:

   https://bugs.launchpad.net/horizon/+bug/1033829

(hence the "medium" as opposed to "low" severity).

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/17805
Committed: http://github.com/openstack/nova/commit/4371509084c97072cc5f2fe16fe01f09b81b1af0
Submitter: Jenkins
Branch: master

commit 4371509084c97072cc5f2fe16fe01f09b81b1af0
Author: Eoghan Glynn <email address hidden>
Date: Mon Dec 10 19:18:50 2012 +0000

    Consider reserved count in os-user-limits extension

    Fixes bug 1088606

    Previously, the reserved count was not considered in the
    total<Resource>Used values returned, leading to a potentially
    inaccurate view of the actual headroom available when resource
    creation was in-flight.

    Now, the reserved count is optionally included, controlled
    by a new 'reserved' query parameter.

    Change-Id: If71ac6f8e428b58b7c80c67ad99124e4233102d1