Revert "[SPARK-4183] Enable NettyBlockTransferService by default"

This reverts commit 59e626c701227634336110e1bc23afd94c535ede.
[SPARK-4121] Set commons-math3 version based on hadoop profiles, instead of shading

In #2928 , we shade commons-math3 to prevent future conflicts with hadoop. It caused problems with our Jenkins master build with maven. Some tests used local-cluster mode, where the assembly jar contains relocated math3 classes, while mllib test code still compiles with core and the untouched math3 classes.

This PR sets commons-math3 version based on hadoop profiles.

pwendell JoshRosen srowen

Author: Xiangrui Meng <meng@databricks.com>

Closes #3023 from mengxr/SPARK-4121-alt and squashes the following commits:

580f6d9 [Xiangrui Meng] replace tab by spaces
7f71f08 [Xiangrui Meng] revert changes to PoissonSampler to avoid conflicts
d3353d9 [Xiangrui Meng] do not shade commons-math3
b4180dc [Xiangrui Meng] temp work
[SPARK-4183] Close transport-related resources between SparkContexts

A leak of event loops may be causing test failures.
Enable netty