Metadata persistence in HDFS and MySQL

Partially implements the issue https://github.com/telefonicaid/fiware-connectors/issues/41

100% tests passed
Manual tests passed
Partially fixed in https://github.com/telefonicaid/fiware-connectors/commit/fa48bfbce9a4882253ea19b43c9b85b3be734324 (checking the current row-like provision is only done when running in row mode). The column-like provision is postponed for a better analysis.