mysql-test: allow suite.pm add its suite to the default list.

run tokudb suites by default.
mark big and slow tests tokudb.change_column_all_1000_1 and
tokudb.change_column_all_1000_10 test as --big

mysql-test/lib/My/Suite.pm

@@ -3,6 +3,7 @@
 
 package My::Suite;
 
+sub is_default { 0 }
 sub config_files { () }
 sub servers { () }
 sub skip_combinations { () }