Proposed blueprint to allow image to be passed during rescue.

This blueprint would allow an additional parameter 'rescue_image_ref'
to be passed as part of the rescue API call.

Part of blueprint allow-image-to-be-specified-during-rescue

Change-Id: Idbfebe8cdeaad667ad33736d8b984f745bfe477d
Merge "Proposed blueprint to allow image to be passed during rescue."