tabletserver: execution plan change

It appears that the MariaDB optimizer is not good at handling
tuple equalities for update statements. This cl changes the exection
plan of all tuple equalities from:
where (pk1, pk2) = (:v1, :v2) or (pk1, pk2) = (:v3, :v4) to
where (pk1 = :v1 and pk2 = :v2) or (pk1 = :v3 and pk2 = :v4), etc.