SPARK-782 Clean up for ASM dependency.

This makes two changes.

1) Spark uses the shaded version of asm that is (conveniently) published
   with Kryo.
2) Existing exclude rules around asm are updated to reflect the new groupId
   of `org.ow2.asm`. This made all of the old rules not work with newer Hadoop
   versions that pull in new asm versions.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #100 from pwendell/asm and squashes the following commits:

9235f3f [Patrick Wendell] SPARK-782 Clean up for ASM dependency.