Tests: dependency on xtradb for some tests

These features are defined only in XtraDB:
  chaged_page_bitmaps,
  innodb_changed_pages

mysql-test/suite/innodb/t/innodb_skip_innodb_is_tables.test

 --source include/not_embedded.inc
+--source include/have_xtradb.inc
 
 select * from information_schema.innodb_trx;
 select * from information_schema.innodb_locks;

mysql-test/t/mysqld--help.test

@@ -4,6 +4,7 @@
 --source include/not_embedded.inc
 --source include/have_perfschema.inc
 --source include/platform.inc
+--source include/have_xtradb.inc
 
 #
 # force lower-case-table-names=1 (linux/macosx have different defaults)