Improve filter scheduler capacity update information

[John Griffith]

Recent improvement/speed-ups to Tempest test exposed a race-condition in volume delete/create sequences where the capabilities update interval of 60 seconds is not sufficient.

We should look at adjusting the polling interval for the gate tests for this and also possibly consider doing a forced update when we encounter no hosts available from the filter scheduler and retry just to avoid any false errors here.

[Giulio Fidente (gfidente)]

A different approach I would suggest is: given that free_capacity_gb seems to be downsized every time a new volume is allocated (before the volume update interval comes into play), it should also be upsized every time a volume is deleted.

[John Griffith (john-griffith)]

Indeed, that's probably the correct approach

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/29599

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/29599
Committed: http://github.com/openstack/cinder/commit/642526013c855e88873ecb96e8680698e095d83a
Submitter: Jenkins
Branch: master

commit 642526013c855e88873ecb96e8680698e095d83a
Author: John Griffith <email address hidden>
Date: Fri May 17 14:03:38 2013 -0600

    Update/Publish volume service updates on delete.

    The Filter scheduler weighing function was failing because
    we were only updating the capacity info either on the periodic
    60 second interval or after succesful creates.

    The result was that if you exceeded your capacity within the
    update interval you would no longer be able to create volumes even
    if you deleted existing volumes until the update was performed and
    published.

    Since we're updating on on create, there's no reason why we shouldn't
    do the same on delete for the applicable volume-service.

    The periodic updates are still important for other purposes so they're left
    alone, but with this change we keep things up to date so the filter scheduler
    has the correct picture of the world.

    Fixes bug: 1180976

    Change-Id: Ic551f512c5a0cf51bafa8b60f0b6b7debbe22692