Cache files created by (specially designed) annotation processors.

These annotation processors (so far, only twitter.common.args) write a file into META-INF which lists all of the files they created. Make pants process that file to decide which files should go in the artifact cache.

Testing Done:
Ran integration tests.

Bugs closed: 132

Reviewed at https://rbcommons.com/s/twitter/r/1250/
Sync of https://github.com/pantsbuild/pants/commit/d365f9119a105f45f60f850fc8921a811f1bc52a