qemu: fix domain startup failing with 'strict' mode in numatune

If the memory mode is specified as 'strict' and with one node, we
get the following error when starting domain.

error: Unable to write to '$cgroup_path/cpuset.mems': Device or resource busy

XML is configured with numatune as follows:
  <numatune>
    <memory mode='strict' nodeset='0'/>
  </numatune>

It's broken by Commit 411cea63
which moved qemuSetupCgroupForEmulator() before setting cpuset.mems
in qemuSetupCgroupPostInit.

Directory '$cgroup_path/emulator/' is created in qemuSetupCgroupForEmulator.
But '$cgroup_path/emulator/cpuset.mems' it not set and has a default value
(all nodes, such as 0-1). Then we setup '$cgroup_path/cpuset.mems' to the
nodemask (in this case it's '0') in qemuSetupCgroupPostInit. It must fail.

This patch makes '$cgroup_path/emulator/cpuset.mems' is set before
'$cgroup_path/cpuset.mems'. The action is similar with that in
qemuDomainSetNumaParamsLive.
Signed-off-by: NWang Rui <moon.wangrui@huawei.com>

src/qemu/qemu_cgroup.c

@@ -611,6 +611,7 @@ static int
 qemuSetupCpusetMems(virDomainObjPtr vm,
                     virBitmapPtr nodemask)
 {
+    virCgroupPtr cgroup_temp = NULL;
     qemuDomainObjPrivatePtr priv = vm->privateData;
     char *mem_mask = NULL;
     int ret = -1;
@@ -627,13 +628,16 @@ qemuSetupCpusetMems(virDomainObjPtr vm,
                                             &mem_mask, -1) < 0)
         goto cleanup;
 
-    if (mem_mask &&
-        virCgroupSetCpusetMems(priv->cgroup, mem_mask) < 0)
-        goto cleanup;
+    if (mem_mask)
+        if (virCgroupNewEmulator(priv->cgroup, false, &cgroup_temp) < 0 ||
+            virCgroupSetCpusetMems(cgroup_temp, mem_mask) < 0 ||
+            virCgroupSetCpusetMems(priv->cgroup, mem_mask) < 0)
+            goto cleanup;
 
     ret = 0;
  cleanup:
     VIR_FREE(mem_mask);
+    virCgroupFree(&cgroup_temp);
     return ret;
 }