Remove Typesafe Config usage and conf files to fix nested property names

With Typesafe Config we had the subtle problem of no longer allowing
nested property names, which are used for a few of our properties:
http://apache-spark-developers-list.1001551.n3.nabble.com/Config-properties-broken-in-master-td208.html



This PR is for branch 0.9 but should be added into master too.
(cherry picked from commit 34e911ce)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>