bug-984057 Tests for --preserve-triggers

t/pt-online-schema-change/samples/sakila_triggers.sql

@@ -0,0 +1,9 @@
+USE sakila;
+CREATE TRIGGER triggers_migration_test
+BEFORE
+-- a comment here
+  INSERT ON film 
+-- just to make things harder
+  FOR EACH ROW SET NEW.length = 60  
+-- for pt_osc
+;