qemu: fix set vcpus on host without NUMA

We don't have to modify cpuset.mems on hosts without NUMA.  It also
fixes an error message that you get instead of success if you trying
update vcpus of a guest on a host without NUMA.

error: internal error: NUMA isn't available on this host
Signer-off-by: NPavel Hrdina <phrdina@redhat.com>

src/qemu/qemu_driver.c

@@ -4890,7 +4890,8 @@ qemuDomainSetVcpusFlags(virDomainPtr dom, unsigned int nvcpus,
                                         &persistentDef) < 0)
         goto endjob;
 
-    if (flags & VIR_DOMAIN_AFFECT_LIVE && !(flags & VIR_DOMAIN_VCPU_GUEST)) {
+    if (flags & VIR_DOMAIN_AFFECT_LIVE && !(flags & VIR_DOMAIN_VCPU_GUEST) &&
+        virNumaIsAvailable()) {
         if (virCgroupNewEmulator(priv->cgroup, false, &cgroup_temp) < 0)
             goto endjob;