[SPARK-959] Explicitly depend on org.eclipse.jetty.orbit jar

Without this, in some cases, Ivy attempts to download the wrong file
and fails, stopping the whole build. See bug for more details.

(This is probably also the beginning of the slow death of our
recently prettified dependencies. Form follow function.)
Merge pull request #183 from aarondav/spark-959

[SPARK-959] Explicitly depend on org.eclipse.jetty.orbit jar

Without this, in some cases, Ivy attempts to download the wrong file and fails, stopping the whole build. See [bug](https://spark-project.atlassian.net/browse/SPARK-959) for more details.

Note that this may not be the best solution, as I do not understand the root cause of why this only happens for some people. However, it is reported to work.