FIX compount persistence in CKAN

Solves the bug reported by Juan Elosua.

The user has tested this branch and reported sucessfully.
The attrValue is originally obtained here:
https://github.com/telefonicaid/fiware-connectors/blob/bug/compound_persistence_ckan/flume/src/main/java/es/tid/fiware/fiwareconnectors/cygnus/sinks/OrionCKANSink.java#L186

At that point, simply use <code>getContextValue(<b>true</b>)</code>. Passing "true" means "give me a Java string starting and ending with a quote if the Json element is not an array or a vector, i.e. it is a Json string". Passing "false" means "independently of the type of the Json element, return me a Java string not starting and not ending with a quote".

(note: It is important to distinguish between Java string and Json string)

Being said that and given the code works... it is up to you to test the <code>getContextValue(<b>true</b>)</code> :)