Merge pull request #846 from shinnok/bb-5.5-mtr-shm

MDEV-17022: check if mtr --mem location is writeable

mysql-test/mysql-test-run.pl

@@ -1457,7 +1457,7 @@ sub command_line_setup {
 
     foreach my $fs (@tmpfs_locations)
     {
-      if ( -d $fs )
+      if ( -d $fs && -w $fs )
       {
 	my $template= "var_${opt_build_thread}_XXXX";
 	$opt_mem= tempdir( $template, DIR => $fs, CLEANUP => 0);