Add the MySQL connector as a pom dependency

Fixes the issue https://github.com/telefonicaid/fiware-connectors/issues/78

100% tests passed.
Manually tested and working.
In fact, there were 6 or 7 references :s

Fixed in https://github.com/telefonicaid/fiware-connectors/commit/6520c4aa133faf4ad8206dbdd65314eec33391e3