Config updates for the new shuffle transport.

Author: Reynold Xin <rxin@databricks.com>

Closes #3657 from rxin/conf-update and squashes the following commits:

7370eab [Reynold Xin] Config updates for the new shuffle transport.

(cherry picked from commit 9bd9334f588dbb44d01554f9f4ca68a153a48993)
Signed-off-by: Aaron Davidson <aaron@databricks.com>