fix/Kafka destination doesn't send messages

[hubert-rutkowski85]

Changed:

• the credentials weren't decoded before using (which resulted in OK in precheck, and silent fail when uploading)
• checking for existence of topic, in uploader precheck
• when pushing messages, iterate while the producer queue is not empty
• fix not reacting to errors when pushing messages
• kafka lib is logging through unstructured logger (should solve elasticsearch not showing correct loglevel)
• refactored the kafka tests to separate cloud and local files
• some cleaning of code