Fixes #1439. Fixes metabuild downloading unused Scala 2.10.2

Fixes #1439 

Scala instance is added to the Ivy graph via autoLibraryDependency. For metabuilds, scala-library is scoped under “provided” configuration, which does not seem to evict modules on “compiled” configuration.

This PR turns `overrideScalaVersion` flag to `true` for the metabuilds, so override rules are added for the following modules:

- scala-library
- scala-compiler
- scala-reflect

/review @havocp 
this makes me say "why is scala-reflect a string literal and the other two are symbols" - is there a good reason?