Skip detecting placement if controller is disabled

If the app has provided a whitelist of controllers to be used,
we skip detecting its mount point. We still, however, fill in
the placement info which later confuses the machine name
validation code. Skip detecting placement if the controller
mount point is not set
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/util/vircgroup.c

@@ -137,8 +137,8 @@ virCgroupValidateMachineGroup(virCgroupPtr group,
 
         if (STRNEQ(tmp, name) &&
             STRNEQ(tmp, partname)) {
-            VIR_DEBUG("Name '%s' does not match '%s' or '%s'",
-                      tmp, name, partname);
+            VIR_DEBUG("Name '%s' for controller '%s' does not match '%s' or '%s'",
+                      tmp, virCgroupControllerTypeToString(i), name, partname);
             goto cleanup;
         }
     }
@@ -426,7 +426,8 @@ static int virCgroupDetectPlacement(virCgroupPtr group,
                  * selfpath=="/libvirt.service" + path="" -> "/libvirt.service"
                  * selfpath=="/libvirt.service" + path="foo" -> "/libvirt.service/foo"
                  */
-                if (typelen == len && STREQLEN(typestr, tmp, len)) {
+                if (typelen == len && STREQLEN(typestr, tmp, len) &&
+                    group->controllers[i].mountPoint != NULL) {
                     if (virAsprintf(&group->controllers[i].placement,
                                     "%s%s%s", selfpath,
                                     (STREQ(selfpath, "/") ||