Comment 6 for bug 1817385

Reviewed: https://review.openstack.org/642613
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=29d42fa73448b3d23d9da4db7b2f407694681ece
Submitter: Zuul
Branch: stable/queens

commit 29d42fa73448b3d23d9da4db7b2f407694681ece
Author: Ryan Liang <email address hidden>
Date: Mon Feb 25 17:43:46 2019 +0800

    VNX: update sg in cache

    When `destroy_empty_storage_group` is enabled, the sg will be deleted
    after the last lun is detached from it. The issue is that the sg cache
    isn't updated, which caused the failure of subsequent attaching volumes
    to the same host because the sg in the cache will be used directly which
    doesn't exist any more.

    The fix is updating the sg with poll after deleting it. This doesn't
    delete the sg from cache explicitly but makes sure the sg in cache with
    latest status `not-exist`. Subsequent attaching will create the sg if it
    is `not-exist`.

    Closes-bug: #1817385
    Change-Id: Ibb39879a77c97c6a5d885461e93116810d16b265
    (cherry picked from commit eefd8302b3a01fd5cff0169b6eca0588975ff244)
    (cherry picked from commit 1f57f502c893a840ee5021fbca36ae95eed50e73)