bug/191

Fixes issue https://github.com/telefonicaid/fiware-connectors/issues/191
An example:

    time=2014-09-15T15:54:16.979CEST | lvl=DEBUG | trans=1410789250-775-0000000000 | function=persist | comp=Cygnus | msg=es.tid.fiware.fiwareconnectors.cygnus.sinks.OrionHDFSSink[299] : [hdfs-sink1] Processing
context attribute (name=temperature, type=centigrade)