docker plugin should require JavaAppPackaging

[MasseGuillaume]

https://github.com/sbt/sbt-native-packager/blob/master/src/main/scala/com/typesafe/sbt/packager/docker/DockerPlugin.scala#L66

I need to add JavaAppPackaging manually or it fails with opt folder not found

[muuki88]

This is by design. DockerPlugin is just an output format you can choose. JavaAppPackaging enables the DockerPlugin. If you only enable the DockerPlugin you are responsible for setting up your application yourself. Because that's a common problem, we have the archetypes, which do all the heavy lifting for you.

[MasseGuillaume]

Maybe we should document this http://www.scala-sbt.org/sbt-native-packager/formats/docker.html