qemu: Don't try to fetch migration stats on destination

Migration statistics are not available on the destination host and
starting a query job during incoming migration is not allowed. Trying to
do that would result in

    Timed out during operation: cannot acquire state change lock (held
    by remoteDispatchDomainMigratePrepare3Params)

error. We should not even try to start the job.

https://bugzilla.redhat.com/show_bug.cgi?id=1278727Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

src/qemu/qemu_driver.c

@@ -12992,9 +12992,16 @@ qemuDomainGetJobStatsInternal(virQEMUDriverPtr driver,
     if (!priv->job.current || !priv->job.current->stats.status)
         fetch = false;
 
-    if (fetch &&
-        qemuDomainObjBeginJob(driver, vm, QEMU_JOB_QUERY) < 0)
+    if (fetch) {
+        if (priv->job.asyncJob == QEMU_ASYNC_JOB_MIGRATION_IN) {
+            virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                           _("migration statistics are available only on "
+                             "the source host"));
+            return -1;
+        }
+        if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_QUERY) < 0)
             return -1;
+    }
 
     if (!completed &&
         !virDomainObjIsActive(vm)) {