Comment 4 for bug 1657585

Reviewed: https://review.openstack.org/429476
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=70afc0d5408aaae8beb587682fe26c124c0cacee
Submitter: Jenkins
Branch: master

commit 70afc0d5408aaae8beb587682fe26c124c0cacee
Author: Matt Riedemann <email address hidden>
Date: Sun Feb 5 16:32:44 2017 -0500

    Handle conflicts for os-assisted-volume-snapshots

    Since a guest-assisted disk snapshot is performed on the compute
    that the instance is running on, there are only certain states
    that the instance can be in to perform this operation. For example,
    if the instance is shelved_offloaded then the instance does not
    have a host and we can't cast to a compute to perform the snapshot.

    Given how unrestrictive this API was before, the only restriction
    we place on the state is that the instance does not have a task_state
    set. We allow any vm_state for performing the operation as long as
    there is a host and no task_state.

    As noted in the code, we'd normally return a 409 in this case but
    according to our microversion docs [1] that would be a new error
    code and require a version bump, so this change just uses 400 and
    leaves a TODO to make this 409 in a later mass return code update
    microversion.

    [1] https://docs.openstack.org/developer/nova/api_microversion_dev.html#f1

    Change-Id: I1dc54a38f02bb48921bcbc4c2fdcc2c946e783c1
    Closes-Bug: #1657585