Ability to abandon/cancel disk import

The action is meant to allow user to remove a disk that can't finish blocks import for any reasons. What happens behind the scenes may be similar to a combination of bulk-write-stop and finalize actions. This may be more a need for the CLI because it obscures the need to manage the granular actions/states, to the extent that when the import fails to complete, user may not know what to do with a disk that is taking up space but cannot be deleted.

I've putting this as a post-MVP requirement and will document the disk state diagrams like the following in the user guide and augment them with instructions for handling disk deletion.

Start with the existing bulk-write-stop and finalize actions, then review the disk-create and disk-use state diagrams linked in the issue. Determine how a failed import should be abandoned so the disk can be deleted, and whether the CLI should hide the granular state handling. Update the user guide with the resulting disk-deletion instructions.