Fix the image file storage type

Refactor all the storage code so that we can persist data between
storage functions, meaning we don't have to use kpartx -l for image
files, which breaks regularly
Merge branch 'imagesfix' into HEAD

* imagesfix:
  Fix the image file storage type

Conflicts:
	lib/provision/storage/image.rb
	lib/provision/storage/local.rb
	lib/provision/storage/service.rb