Aligned the Scala KMeans with the Java KMeans example.

Some fixes in the Scala KMeans example to unify the Scala with the Java example so both behave the same. This should avoid unnecessary confusion when people try the [Quick Start Guide](http://stratosphere.eu/quickstart/example.html) with the Scala version instead.

PS. I'm not sure whether the Scala KMeans job is currenly used for integration testing. If yes, the IT test cases should be adapted before merge as well.