The test is for a bug that was introduced in MySQL 5.7.18
but not MariaDB 10.2, because MariaDB did not merge the change
that was considered incomplete and too risky for a GA release:

Bug#23481444 OPTIMISER CALL ROW_SEARCH_MVCC() AND READ THE INDEX
APPLIED BY UNCOMMITTED ROWS

So, we are only merging the test changes from the bug fix in MySQL 5.7.19,
not any code changes:

commit 4f86aca37d551cc756d9187ec901f8c4a68a0543
Author: Thirunarayanan Balathandayuthapani <thirunarayanan.balathandayuth@oracle.com>
Date:   Wed Apr 26 11:10:41 2017 +0530

    Bug #25793677   INNODB: FAILING ASSERTION: CLUST_TEMPL_FOR_SEC || LEN