Comment 8 for bug 1803498

Reviewed: https://review.openstack.org/648610
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=14e9e1ef868759df2be67f7b61ce3c41ec547ac2
Submitter: Zuul
Branch: stable/queens

commit 14e9e1ef868759df2be67f7b61ce3c41ec547ac2
Author: Abhishek Kekane <email address hidden>
Date: Wed Mar 13 18:12:42 2019 +0000

    Data remains in staging area if 'file' store is not enabled

    When operator has not enabled 'file' store and using other stores like ceph,
    swift etc. the uploading to staging area works as we explicitly
    build 'file' store during this operation, while cleaning up we directly
    use 'glance_store.delete_from_backend' which only works if 'file'
    store is enabled.

    Modified '_DeleteFromFS' task and _unstage call which will use os
    module to unlink the file present in staging area explicitly to
    delete the data from staging area.

    Conflicts:
           glance/async/flows/api_image_import.py
           glance/tests/unit/async_/flows/test_web_download.py

    NOTE: async_ module was not available in queens so renamed
    the module name to async.

    Closes-Bug: #1803498
    Change-Id: If0b3b0af9300301291758c67267890e0959ebb3c
    (cherry picked from commit c92724608512d42b56152d199cc0fea049e4d4a7)