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 change (make overrideScalaVersion apply to scala-reflect also) seems logically distinct from making the metabuild set overrideScalaVersion - this will apply to the regular build too not just the metabuild right? (assuming the regular build sets overrideScalaVersion)

Which is fine, but potentially it could have been a separate commit