Driver relies on server default collation.

Since https://jira.mariadb.org/browse/CONJ-597 driver always use UTF8MB4 collation.
If server use utf8mb4 collation (collation_server), connector will use that collation (collation_connection).
If the server doesn't use utf8mb4 collation, the connector will force the use of utf8mb4_unicode_ci collation.

when a server is configured to use a utf8mb3 != than unicode, some query might result is Illegal mix of collations (utf8mb4_XXX_ci,COERCIBLE) and (utf8mb4_YYYY_ci,COERCIBLE) for operation '<>'). The server automatically handle utf8mb4 / utf8mb3 conversion, so before CONJ-597 change, so server configured in utf8 collation different than unicode may result in this issue.

The goal of this task is that upgrade of driver doesn't change compare to previous behaviour.
(when server send utf8mb3, client must use equivalent utf8mb4 collation)