Replace removed check for innodb support through server variables

Since MySQL 5.6.1, the server variable `have_innodb` has been removed. The command `SHOW ENGINES` instead is supported since MySQL 4.1.

See http://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html#sysvar_have_innodb

This patch replaces the server variable check with the recommended way through `SHOW ENGINES`.

I did think about `strtolower`ing the keys and values, but I checked that the spelling has always been the same since MySQL 4.1.

Cheers
:octocat: Jérôme
https://jira.ez.no/browse/EZP-21006