Spark-939: allow user jars to take precedence over spark jars

I still need to do a small bit of re-factoring [mostly the one Java file I'll switch it back to a Scala file and use it in both the close loaders], but comments on other things I should do would be great.

Author: Holden Karau <holden@pigscanfly.ca>

Closes #217 from holdenk/spark-939-allow-user-jars-to-take-precedence-over-spark-jars and squashes the following commits:

cf0cac9 [Holden Karau] Fix the executorclassloader
1955232 [Holden Karau] Fix long line in TestUtils
8f89965 [Holden Karau] Fix tests for new class name
7546549 [Holden Karau] CR feedback, merge some of the testutils methods down, rename the classloader
644719f [Holden Karau] User the class generator for the repl class loader tests too
f0b7114 [Holden Karau] Fix the core/src/test/scala/org/apache/spark/executor/ExecutorURLClassLoaderSuite.scala tests
204b199 [Holden Karau] Fix the generated classes
9f68f10 [Holden Karau] Start rewriting the ExecutorURLClassLoaderSuite to not use the hard coded classes
858aba2 [Holden Karau] Remove a bunch of test junk
261aaee [Holden Karau] simplify executorurlclassloader a bit
7a7bf5f [Holden Karau] CR feedback
d4ae848 [Holden Karau] rewrite component into scala
aa95083 [Holden Karau] CR feedback
7752594 [Holden Karau] re-add https comment
a0ef85a [Holden Karau] Fix style issues
125ea7f [Holden Karau] Easier to just remove those files, we don't need them
bb8d179 [Holden Karau] Fix issues with the repl class loader
241b03d [Holden Karau] fix my rat excludes
a343350 [Holden Karau] Update rat-excludes and remove a useless file
d90d217 [Holden Karau] Fix fall back with custom class loader and add a test for it
4919bf9 [Holden Karau] Fix parent calling class loader issue
8a67302 [Holden Karau] Test are good
9e2d236 [Holden Karau] It works comrade
691ee00 [Holden Karau] It works ish
dc4fe44 [Holden Karau] Does not depend on being in my home directory
47046ff [Holden Karau] Remove bad import'
22d83cb [Holden Karau] Add a test suite for the executor url class loader suite
7ef4628 [Holden Karau] Clean up
792d961 [Holden Karau] Almost works
16aecd1 [Holden Karau] Doesn't quite work
8d2241e [Holden Karau] Adda FakeClass for testing ClassLoader precedence options
648b559 [Holden Karau] Both class loaders compile. Now for testing
e1d9f71 [Holden Karau] One loader workers.