Add a HDFS files translator from version 0.1 to version 0.3

This PR implements the issue https://github.com/telefonicaid/fiware-connectors/issues/65 and fix the original translator (0.1->0.2).
Good catch!

Maybe by using a reserved word such as "NULL"? Other aproaches suggest to use an empty string (""), and check its length:
http://stackoverflow.com/questions/3061036/how-to-find-variable-is-empty-or-in-shell-script

If using "", I think it is automatically resoved, but I'll test it.

What do you think?