cgroup: Add missing errno == ENOENT check in virCgroupRemoveRecursively

ENOENT happens normally when a subsystem is enabled with any other
subsystems and the directory of the target group has already removed
in a prior loop. In that case, the function should just return without
leaving an error message.

NB this is the same behavior as before introducing virCgroupRemoveRecursively.

src/util/cgroup.c

@@ -616,6 +616,8 @@ static int virCgroupRemoveRecursively(char *grppath)
 
     grpdir = opendir(grppath);
     if (grpdir == NULL) {
+        if (errno == ENOENT)
+            return 0;
         VIR_ERROR(_("Unable to open %s (%d)"), grppath, errno);
         rc = -errno;
         return rc;