[libvirt] Odd implementation of libvirt qemudDomainSetMaxMemory

Hey Cole, In commit 09a33fd8a9cc85e5e1064168472bff7aecff15fb, you made it so that qemudDomainSetMaxMemory() was hotplug only. However, with the changes you pushed, this function no longer makes a lot of sense. It looks up the domain, checks to make sure it is active, and then if it is active, it fails. Assuming that qemu doesn't support changing the maximum amount of memory on the fly, wouldn't it be better to just remove this function entirely and let the higher libvirt layers report "function not supported"? -- Chris Lalancette