Add stable public methods for image name and path
Add stable public methods for image name and path

As discussed in issue #33 the `guest.name` and `guest.diskimage` are
considered internal and should not be accessed by third parties.

This provides methods `guest.image_name` and `guest.output_image_path`
that provide the same functionality but are available to everyone.

Signed-off-by: Tomas Sedovic <2bc6038c3dfca09b2da23c8b6da8ba884dc2dcc2@sedovic.cz>

clalancette/oz,NeilBryant/oz,cernops/oz,imcleod/oz,moofrank/oz,nullr0ute/oz,mgagne/oz,nullr0ute/oz,cernops/oz,ndonegan/oz,imcleod/oz,ndonegan/oz,mgagne/oz,NeilBryant/oz,moofrank/oz,clalancette/oz