Don't ignore image changes in skeleton terraform lifecycle

[sjpb]

Allows the skeleton terraform to act on image changes. This is because:

• Now state is not in the root disk, being able to reimage with terraform is useful, especially for development.
• No one is using slurm-controlled reimage (which conflicts with terraform tracking compute node usage)
• For the control node, there are issues around lifecycle due to the root disk block device definition also referencing the image.
• For production non-Azimuth use, any change to lifecycle needs some careful consideration anyway.