[libvirt] virsh setmaxmem

All, My recent patch to remove qemudDomainSetMaxMem() revealed some surprising (to me) behavior of "virsh setmaxmem". In particular, if you run setmaxmem, and the hypervisor doesn't support it, this fact will be reported to you. However, if the amount you were setting for maxmem happens to be lower than "currentMemory", setmaxmem will silently balloon down the domain for you. This is a surprising result exactly because virsh reports error, but did something anyway. What I would expect is that if a hypervisor doesn't support virDomainSetMaxMem(), nothing at all is done. If we agree that this is behavior that needs to be fixed, I would suggest that we move the code to do the auto-ballooning into each of the individual drivers that *do* support virDomainSetMaxMem(). Currently that includes the test driver, the LXC driver, and the Xen driver. This way, we maintain the current behavior for the hypervisors that support this call, and make sure not to do anything at all for the hypervisors that do not. Opinions? -- Chris Lalancette