* elastic now provides a fully opensource version for their prebuild
docker images (elasticsearch, kibana and so on). To avoid running into
licensing conflicts for this addon example, we should rather use these
images instead of the premium ones (were we also have to disable premium
features manually right now)
* remove disable flags for xpack, since *-oss images do not include this anymore
* bump elasticsearch and kibana version from 5.6.4 to 6.2.4
* use oss version from elastic as baseimg for kibana and elasticsearch
* bump fluentd version to ~>1.1.3
* bump gem 'fluent-plugin-elasticsearch' to '~>2.9.1' to allow usage of elasticsearch 6.x
* bump fluentd-es-image to v2.1.0
* fix elasticserach run.sh to align with new elasticsearch upstream container structure
