qemu: process: Clear priv->namespaces on VM shutdown

Otherwise the private data entry would be kept across instances of the
same VM even if it's not configured to do so.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1453142

src/qemu/qemu_process.c

@@ -6449,6 +6449,10 @@ void qemuProcessStop(virQEMUDriverPtr driver,
     /* clean up migration data */
     VIR_FREE(priv->migTLSAlias);
 
+    /* clear previously used namespaces */
+    virBitmapFree(priv->namespaces);
+    priv->namespaces = NULL;
+
     /* The "release" hook cleans up additional resources */
     if (virHookPresent(VIR_HOOK_DRIVER_QEMU)) {
         char *xml = qemuDomainDefFormatXML(driver, vm->def, 0);