test: use number instead of name in --error

Because "--error WXXX" style is supported only by MariaDB 10.0. Older
MySQL/MariaDB supports only "--error EXXX". We want to use these tests
with all MySQL/MariaDB. So we use "--error NUMBER" instead of "--error
WXXX".

TODO: If all test target MySQL/MariaDB supports "--error WXXX" style,
we should use it.