REST-113. Sets up load testing assembly properly.

Previously a single jar was being generated.
Now we have an assembled tarball.
Dependencies go in the lib/ subdirectory of the tarball.
Bash scripts for running tests go in bin/.
JMeter test plans go in test-plans/.

issue: https://jira.kiji.org/browse/REST-113
review: https://review.kiji.org/r/1729