Volume attach /detach should be blocked during some opertaions

[Phil Day]

Currently volume attach, detach, and swap check on vm_state but not task_state. This means that, for example, volume attach is allowed during a reboot, rebuild, or migration.

As with other operations the check should be against a task state of "None"

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/70377

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/70377
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=a70c5eb83d14541c2297b6d834dff1c0ac00962e
Submitter: Jenkins
Branch: master

commit a70c5eb83d14541c2297b6d834dff1c0ac00962e
Author: Phil Day <email address hidden>
Date: Fri Jan 31 16:53:35 2014 +0000

    Volume operations should be blocked for non-null task state

    Currently volume attach, detach, and swap check on vm_state but
    not task_state. This means that, for example, volume attach is
    allowed even when other operations such as migration are in
    progress. As with other operations the check should be against
    a task state of "None"

    This change also refactors the volume_attach() method a little
    so that the cells api can include the state decorator checks.

    Change-Id: I0c4d697cf9d9e431a050c3c1b03e46b8629d182a
    Closes-Bug: #1274627