virt-sandbox-image: smarter source name computing
virt-sandbox-image: smarter source name computing

To compute the source class name from the URI scheme, we need to be a
bit smarter to have a nice scheme for sources like the virt-builder one.
In order to have a scheme like virt-builder:// and a class name like
VirtBuilderSource, strip the non-word characters from the scheme and
camel case the words.

libvirt/libvirt-sandbox,agx/libvirt-sandbox-debian,agx/libvirt-sandbox-debian,libvirt/libvirt-sandbox,agx/libvirt-sandbox-debian,agx/libvirt-sandbox-debian,libvirt/libvirt-sandbox,agx/libvirt-sandbox-debian