Adds helper to copy a specified disk image for the persistent partition
Adds helper to copy a specified disk image for the persistent partition

Docker-DCO-1.1-Signed-off-by: Isaac Boehman <admin@yacn.pw> (github: yacn)

vmware/boot2docker-cli,moxiegirl/boot2docker-cli,tianon/boot2docker-cli,tianon/boot2docker-cli,moxiegirl/boot2docker-cli,boot2docker/boot2docker-cli,nathanleclaire/boot2docker-cli,vmware/boot2docker-cli,boot2docker/boot2docker-cli,beni55/boot2docker-cli,SvenDowideit/boot2docker-cli,mattrobenolt/boot2docker-cli,beni55/boot2docker-cli,SvenDowideit/boot2docker-cli,mattrobenolt/boot2docker-cli,nathanleclaire/boot2docker-cli