Update kafka_package_name to confluent-kafka-2.12

[TJM]

In

puppet-confluent/manifests/params.pp

Line 174 in 9bc2da5

$kafka_package_name = 'confluent-kafka-2.11'

, it hardcodes a specific (outdated) version of the confluent-kafka package. We suggest that it should be updated to 2.12. I am not sure why the version number is embedded into the package name, as that makes maintenance a pain, but whatever :)

~tommy