Skip perfschema.misc if "var" is a symlink (due to Bug 51447).

mysql-test/include/not_var_link.inc

+# Test if MYSQLTEST_VARDIR is a soft link
+# If we run in parallel, we have a suffix "/$child_num", so chop off that.
+
 perl;
+  my $path= $ENV{'MYSQLTEST_VARDIR'};
+  $path=~ s|/\d+$||;
   open (ISLINK, ">" . $ENV{'MYSQL_TMP_DIR'} . "/mtr_var_link");
-  my $mvr= -l $ENV{'MYSQLTEST_VARDIR'} ? 1 : 0;
+  my $mvr= -l $path ? 1 : 0;
   print ISLINK "let \$mtr_var_link= $mvr;\n";
   close ISLINK;
 EOF