adding json 5.7 tests

localtests/json57/create.sql

@@ -0,0 +1,21 @@
+drop table if exists gh_ost_test;
+create table gh_ost_test (
+  id int auto_increment,
+  j json,
+  primary key(id)
+) auto_increment=1;
+
+drop event if exists gh_ost_test;
+delimiter ;;
+create event gh_ost_test
+  on schedule every 1 second
+  starts current_timestamp
+  ends current_timestamp + interval 60 second
+  on completion not preserve
+  enable
+  do
+begin
+  insert into gh_ost_test values (null, '"sometext"');
+  insert into gh_ost_test values (null, '{"key":"val"}');
+  insert into gh_ost_test values (null, '{"is-it": true, "count": 3, "elements": []}');
+end ;;