Zookeeper benchmark based on zk-smoketest.

Add a watch test and some shell scripts to generate gnuplot data, see result directory.

zookeeper version 3.4.3

results generated on Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, 16G RAM, with default Java heap size 4G.

test_size.sh requires to set Java heap size to 8G, -Xmx8192m