Workaround unhandled rdmsr/wrmsr

Since we use cpu mode='host-model' the guest kernel is probing for different CPU registers. Some of the registers are not (yet) implemented in Qemu/KVM and therefore generate the following warnings in the hosts kernel log when booting a VM:

[72699.462538] kvm [30681]: vcpu0 unhandled rdmsr: 0x345
[72699.465315] kvm_set_msr_common: 22 callbacks suppressed
[72699.465318] kvm [30681]: vcpu0 unhandled wrmsr: 0x680 data 0
[72699.465321] kvm [30681]: vcpu0 unhandled wrmsr: 0x6c0 data 0
[72699.465323] kvm [30681]: vcpu0 unhandled wrmsr: 0x681 data 0
[72699.465325] kvm [30681]: vcpu0 unhandled wrmsr: 0x6c1 data 0
[72699.465328] kvm [30681]: vcpu0 unhandled wrmsr: 0x682 data 0
[72699.465330] kvm [30681]: vcpu0 unhandled wrmsr: 0x6c2 data 0
[72699.465332] kvm [30681]: vcpu0 unhandled wrmsr: 0x683 data 0
[72699.465334] kvm [30681]: vcpu0 unhandled wrmsr: 0x6c3 data 0
[72699.465336] kvm [30681]: vcpu0 unhandled wrmsr: 0x684 data 0
[72699.465339] kvm [30681]: vcpu0 unhandled wrmsr: 0x6c4 data 0

This is not an issue, see for example: https://bugs.launchpad.net/qemu/+bug/1208540

If the warnings should be suppressed, use:

echo 1 > /sys/module/kvm/parameters/ignore_msrs