SPARK-1167: Remove metrics-ganglia from default build due to LGPL issues...

This patch removes Ganglia integration from the default build. It
allows users willing to link against LGPL code to use Ganglia
by adding build flags or linking against a new Spark artifact called
spark-ganglia-lgpl.

This brings Spark in line with the Apache policy on LGPL code
enumerated here:

https://www.apache.org/legal/3party.html#options-optional

Author: Patrick Wendell <pwendell@gmail.com>

Closes #108 from pwendell/ganglia and squashes the following commits:

326712a [Patrick Wendell] Responding to review feedback
5f28ee4 [Patrick Wendell] SPARK-1167: Remove metrics-ganglia from default build due to LGPL issues.
(cherry picked from commit 16788a654246067fd966033b5dc9bc0d4c759b70)

Conflicts:

	core/pom.xml
	dev/audit-release/sbt_app_core/src/main/scala/SparkApp.scala
	dev/create-release/create-release.sh
	pom.xml
	project/SparkBuild.scala
Log4j build fix on 0.9 branch

Spark should include log4j by default. Downstream packagers can exclude log4j
if they want to use another logging backend.