Use our Flume 1.6.0 with fixes.
Remove stratio-decompress-deserializer.

It is unstable and buggy. Will bring it back later.
xmlxpath-deserializer: Update to new Flume API.
Update Apache Flume mirror.
assembly: Remove flume-plugin assembly; exclude unneeded artifacts.
maven: Re-arrange assembly building.
Change flume repo to Stratio fork.
xmlpath-deserializer: Improve tests; support text() extensions.
travis: Do not run Flume tests; update Flume fork.
Add Flume's Kafka Source to dist.