Current & Max memory setting missing for virtualized hosts

[jmaas]

When installing a virtualized host in kvm, the only setting available in cobbler, Virt RAM, is only the maximum memory available to a guest. libvirt/kvm allow a current memory usage setting as well but that one is not possible to configure in cobbler.

Impact: If I need to provision virtual machines with dynamically adjusted memory, I need to set the max in cobbler and then use another too to adjust it and then reboot the vm. This take the provisioning of virtual machines only half way.

Copied from cobbler/cobbler#288