qemu: Update blkio.weight value after successful set

https://bugzilla.redhat.com/show_bug.cgi?id=1253107

Make a call virCgroupGetBlkioWeight to re-read blkio.weight right
after it is set in order to keep internal data up-to-date.
Signed-off-by: NLuyao Huang <lhuang@redhat.com>
(cherry picked from commit bf278821)

src/qemu/qemu_driver.c

@@ -9185,7 +9185,8 @@ qemuDomainSetBlkioParameters(virDomainPtr dom,
             virTypedParameterPtr param = &params[i];
 
             if (STREQ(param->field, VIR_DOMAIN_BLKIO_WEIGHT)) {
-                if (virCgroupSetBlkioWeight(priv->cgroup, param->value.ui) < 0)
+                if (virCgroupSetBlkioWeight(priv->cgroup, param->value.ui) < 0 ||
+                    virCgroupGetBlkioWeight(priv->cgroup, &def->blkio.weight) < 0)
                     ret = -1;
             } else if (STREQ(param->field, VIR_DOMAIN_BLKIO_DEVICE_WEIGHT) ||
                        STREQ(param->field, VIR_DOMAIN_BLKIO_DEVICE_READ_IOPS) ||