mtr: allow nested plugin suites to be defaults too

mysql-test/lib/mtr_cases.pm

@@ -337,15 +337,20 @@ sub parse_disabled {
 #
 sub collect_default_suites(@)
 {
-  my @dirs = my_find_dir(dirname($::glob_mysql_test_dir),
-                         [ @plugin_suitedirs ], '*');
-  for my $d (@dirs) {
-    next unless -f "$d/suite.pm";
-    my $sname= basename($d);
+  use File::Find;
+  my @dirs;
+  find(sub {
+      push @dirs, [$File::Find::topdir, $File::Find::name]
+        if -d and -f "$File::Find::name/suite.pm";
+  }, my_find_dir(dirname($::glob_mysql_test_dir), \@plugin_suitedirs));
+
+  for (@dirs) {
+    my ($plugin_root, $dir) = @$_;
+    my $sname= substr $dir, 1 + length $plugin_root;
     # ignore overlays here, otherwise we'd need accurate
     # duplicate detection with overlay support for the default suite list
     next if $sname eq 'main' or -d "$::glob_mysql_test_dir/suite/$sname";
-    my $s = load_suite_object($sname, $d);
+    my $s = load_suite_object($sname, $dir);
     push @_, $sname if $s->is_default();
   }
   return @_;