Adding status field to image location -- scrubber queue switching

Adding a status field to image's each location property, each location
status can be 'active', 'pending_delete' and 'deleted'.

Under location's status information Scrubber service can make cleanup
based on DB records also but not a dedicated queue-file for each image.

This is fourth part of this change which covered using scrubber DB queue
in store. This change allow cloud admin/operator deploy a central
Scrubber service(s) on one or two hosts only, before this Glance require
deploy it on each API service host since Scrubber only support load
pending delete jobs from local file.

Partially-Implements BP: image-location-status

Change-Id: I6910b55de8c3b203560d75ff3d1675eda31ae786
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Merge "Adding status field to image location -- scrubber queue switching"