WIP: Enable setting Jetty temp directory.

This change allows a user to use the `search.temp_dir` configuration variable to set the temp directory used by Jetty.

See the following issues:
* basho/yokozuna#401
* basho/node_package#150

This is somewhat important as the default causes Solr to write data in directories that shouldn't be written to, like `/usr/local/lib/riak/lib/yokozuna-2.0.0beta1-81-g47214a6/priv/solr` on FreeBSD.

WIP as I'm still getting `riak_test` up and running. I did complete testing a local devrel.