Add an option for migrating images between datastores

[OpenNebulaSupport]

Description
It will be useful for some scenarios to be able to migrate an image between different datastores with or without the same DS_MAD.

Currently oneimage command can clone an image to a different image datastore but that image will have a different ID. The migrate command would keep the image ID moved to a different image datastore. In that case there is the following situation that can lead to problems:

1. A new image datastore is being added and the old one has to be deleted
2. The images are cloned in the new datastore, the old one is deleted
   In this moment
3. VMs that rely on any image on the old datastore images can't be recreated easily (the image that was used to created them does not exist, they don't know about the clone on the new datastore)
4. The database reflects that the images on the old datastore are still being in use by those VMs

The command may also have to update:

• /VM/TEMPLATE/DISK/{DATASTORE,DATASTORE_ID,IMAGE,IMAGE_ID,SOURCE} on the VMs running that depend on the migrated image
• /VMTEMPLATE/TEMPLATE/DISK/{DATASTORE,DATASTORE_ID,SOURCE} on the templates that depend on the migrated image

Use case
The use case for the command would be

oneimage migrate IMAGE_ID --datastore DATASTORE_ID

It should:

1. Check if IMAGE_ID and DATASTORE_ID exist and if DATASTORE_ID is an image datastore
2. Move IMAGE_ID to DATASTORE_ID keeping its IMAGE_ID and name (IMAGE field)
3. Update the fields /IMAGE/{SOURCE,PATH,DATASTORE,DATASTORE_ID} of the image
4. For all the templates that use IMAGE_ID: update the fields /VMTEMPLATE/TEMPLATE/DISK/{DATASTORE,DATASTORE_ID,SOURCE}
5. For all the VMs that depend on IMAGE_ID: update the fields /VM/TEMPLATE/DISK/{DATASTORE,DATASTORE_ID,SOURCE}

After that, the /IMAGE/VMS field of the image should be consistent, and the templates and the vms too

Interface Changes
This option should be available in all the interfaces.

Additional Context
It may be possible that the image source and datastore must be updated somewhere else

Progress Status

• Branch created
• Code committed to development branch
• Testing - QA
• Documentation
• Release notes - resolved issues, compatibility, known issues
• Code committed to upstream release/hotfix branches
• Documentation committed to upstream release/hotfix branches

[Snowmanko]

It would be really usefull. i.e. when upgrading SDS like CEPH / Gluster / DRBD. So plan would be to migrate VMs to another SDS/DS and than upgrade software, after successful upgrade I would be able to bring VMs back for test or production again. So no more worrying about this procedure.

[rsmontero]

Also consider migration across different Ceph Datastores (different pools)