Multitenancy support (HDFS and MySQL)

This PR finishes the implementation of the issue https://github.com/telefonicaid/fiware-connectors/issues/36

100% tests passed
Manually tested

Multitenancy support in HDFS is achieved by implementing the following HDFS folder schema:

    hdfs:///user/<clientUsername>/<organization>/<entityId>-<entityType>/<entityId>-<entityType>.txt

where:

* `clientUsername` is the client username (e.g. valencia, repsol). Whitin the current version, this is the value of the `cosmos_default_username` parameter; in future releases it will be the real client username.
* `organization`refers to the `fiware-service` header.
* `<entityId>-<entityType>` is the usual entity descriptor. In this case, a folder is created and then a file within it; the purpose is to support the creation of per entity Hive tables, and thus a specific folder is required per each entity.

Multitenancy support in MySQL is achieved by implementing the following databse schema:

    mysql:///<organization>/<entityId>-<entityType>

where:

* `organization` refers to the `fiware-service` header, and it is a database.
* `<entityId>-<entityType>` is the usual entity descriptor, and it is a table within the above database.
"(but in future releases it is expected to be given by Orion in the notifications)"... Not sure what do you mean. Maybe we could disscuss it by skype.