Glance-image-recover

Overview
This proposal aims to recover an image which is in 'pending-delete' state so as to provide the revert capability for the purposes of allowing emergency operational action to recover from an accidental delete

General Workflow

 * 1) The 'delayed_delete' config entry is enabled in glance-api.conf
 * 2) Delete the specific image
 * 3) List the images which are 'pending-delete'
 * 4) User PUT /v2/images/{image-uuid} on the requested image to recover it
 * 5) Eventually, the requested image should be in 'active' state after recovering successfully.

REST API
Now in my PoC, I'm using 'PUT' as the REST API method. But TBO, I'm not sure if 'PUT' is a good condidate for image recover, given 'PUT' need to support **Idempotent**. HTTP Request - PUT /v2/images/12345678-1234-1234-1234-123456789abc Response: 200 OK { "status":"active", "name":"cirros-0.3.1-x86_64-uec", "tags":[ ],   "kernel_id":"be50418b-a03c-4947-9122-b80a57f47ac4", "container_format":"ami", "created_at":"2013-11-19T08:42:14Z", "ramdisk_id":"e1256074-9f7b-4067-8356-4a5759c1db11", "disk_format":"ami", "updated_at":"2013-11-19T08:42:16Z", "visibility":"public", "self":"/v2/images/26c16e07-24ca-4abc-a523-bec068012363", "protected":false, "id":"26c16e07-24ca-4abc-a523-bec068012363", "file":"/v2/images/26c16e07-24ca-4abc-a523-bec068012363/file", "checksum":"f8a2eeee2dc65b3d9b6e63678955bd83", "min_disk":0, "size":25165824, "min_ram":0, "schema":"/v2/schemas/image" }

CLI (Glance client)
A new sub command 'image-recover' will be added to Glance python client. Then user can recover an 'pending_delete' image by issuing below command: glance image-recover b55b5e54-b7d8-4629-847f-6f180313db88

Precondition
1. List pending-delete image Current image-list should be extended to support listing the images which in 'pending_delete' status, so that user can get the iamge id to do image recover. 2. Only the image which in 'active' status can be updated to 'pending_delete' After investigated current code, this has been met. See https://review.openstack.org/#/c/53997/ as a reference.