Small fix in virttest.qemu_vm and  shared.unattended

In qemu_vm.py, we get machine type with command "qemu-kvm -M ?", but this command always exit with 1 because not use  escape character; so add escape character in command use '?' to get help info; 

And, add 'lvm2' and 'ethtool' to ubuntu pressed file, because it's required by 'lvm' and 'ethtool' tests;

Thanks,
Xu