Add Serve load testing tool to long running test yaml (#11386)

ci/long_running_tests/ray-project/cluster.yaml

@@ -40,6 +40,8 @@ setup_commands:
     - source activate tensorflow_p36 && pip install -U tensorflow==1.14
     - echo set-window-option -g mouse on > ~/.tmux.conf
     - echo 'termcapinfo xterm* ti@:te@' > ~/.screenrc
+    # Serve load testing tool
+    - 'rm -r wrk || true && git clone https://github.com/wg/wrk.git wrk && cd wrk && make -j && sudo cp wrk /usr/local/bin'
 
     # Uncomment the following if you wish to build Ray instead.
     # - sudo apt-get update