Align os image keys and variables

With the introduction of os-images-info and get-openstack-images we have different variable names doing the same thing. Because of that we use osImages in os-image-server and os_images everywhere else. We need to align this to use camelcase since this was the decision for sylva-core.

Another thing that could be harmonized is the use of standard names for os images produced by os-image-server and the keys under sylva_diskimagebuilder_images so we can drop the transformation of dots into dashes.