[SPARK-7042] [BUILD] use the standard akka artifacts with hadoop-2.x

Both akka 2.3.x and hadoop-2.x use protobuf 2.5 so only hadoop-1 build needs
custom 2.3.4-spark akka version that shades protobuf-2.5

This partially fixes SPARK-7042 (for hadoop-2.x builds)

Author: Konstantin Shaposhnikov <Konstantin.Shaposhnikov@sc.com>

Closes #6341 from kostya-sh/SPARK-7042 and squashes the following commits:

7eb8c60 [Konstantin Shaposhnikov] [SPARK-7042][BUILD] use the standard akka artifacts with hadoop-2.x