I was able to configure it by adding a module with the mysql connector to jboss as7.
It may be the case if you see a message like this in the server log:
New missing/unsatisfied dependencies: service jboss.jdbc-driver.mysql
Check on the following link :
https://zorq.net/b/2011/07/12/adding-a-mysql-datasource-to-jboss-as-7/