Cloned from launchpad blueprint https://blueprints.launchpad.net/glance/+spec/image-location-status.

Description:

Adding status for each image backend storage location to optimize Glance deployment mode. Operator can deploy glance more easy and keep high performance, and using a centralized scrubber service but deploy it on each glance-api node.

1. Add a status field to image location DB entry. Three possible states are 'active', 'pending_delete', and 'deleted'.
2. Keep location status be internal, only display/export locations by API if they are 'active'.
3. The public API doesn't need to change.
4. Image location status migration initially:
image-status => location-status
--------------------------------------------
queued => <None>
saving => <None>
active => active
pending_delete => pending_delete
killed or deleted => deleted
5. Image location status transition DAG diagram:
image upload data or new location(s) added ==>
    'active' status ==> image deleted by api controller ==>
        if CONF.delayed_delete disable ==> delete image  ==> 'deleted' status (end)
                                             |---- enabled ==> schedule delayed delete ==> 'pending_delete' status
                                                                                 ==> Scrubber delete image  ==> 'deleted' status (end)

Specification URL (additional information):

None