[SPARK-1812][wip]

Was just trying out akka 2.3.3 (theoretically it should all work.)
It's safe to ignore the warning if you want to use this kind of parameterized artifactId in your local builds, but we can't do that in the actual Apache source code and release builds.  We may need to start using Maven archetypes (essentially a preprocessing step that will generate the POMs) in order to support cross-compiling for 2.10 and 2.11.