Remove unnecessary bootloader lines in Fedora

Signed-off-by: Chris Lalancette <clalancette@gmail.com>
Add support for Ubuntu 13.04

Signed-off-by: Chris Lalancette <clalancette@gmail.com>
Warn instead of failing when given libvirt_xml with more than one disk

Oz itself never generates libvirt XML with more than one disk.

Allowing users to pass in modified guests at their own risk allows
for some interesting use cases.

The one I'm specifically interested in involves using Image Factory
plus Oz to drive the creation of Live CD images entirely inside of
VMs.
Fixes to improve pylint score

Signed-off-by: Chris Lalancette <clalancette@gmail.com>