Loader [MariaDB]: Set sql_mode in my.cnf.
Since MariaDB 10.2.4, SQL_MODE is by default set to NO_AUTO_CREATE_USER,
NO_ENGINE_SUBSTITUTION, STRICT_TRANS_TABLES, ERROR_FOR_DIVISION_BY_ZERO.
In earlier versions of MariaDB 10.2, and since MariaDB 10.1.7, SQL_MODE
is by default set to NO_ENGINE_SUBSTITUTION, NO_AUTO_CREATE_USER.
For earlier versions of MariaDB 10.1, and MariaDB 10.0 and before, no
default is set.
This change in 10.2 can cause queries to fail, complaining about
no default values:
big_query(): Query failed (Field 'x' doesn't have a default value)
Fixes remainder of [WS-110].