Check special characters in entity and attribute names or types

[frbattid]

As experienced with FINESCE people, if an entity or attribute name or type contains the "/" character then the persisted file for this entity-attribute pair will contain the "/" character. When creating thar file, WebHDFS/HttpFS understands a subdirectory must be created and then a file.

E.g. entity=mycar, entity_tpe=car, attribute_name=speed, attribute_type=km/h will be persisted as mycar-car-speed-km/h.txt, which in the end is the following directory /user/myuser/mystorage/mycar-car-speed-km containing a h.txt file.

Special characters usage must be checked before creating the file name.

[fgalan]

I think to remember that we had some similar issue with other special character in the past, such ":", that gets replaced by _. Probably it is just a matter of including "/" to the list of special characters to check and replace by _.

[fgalan]

Moved to telefonicaid/fiware-connectors#9