This change is a common root for other
Zookeeper related changed regarding
scale-out-scheduler. Zookeeper becoming
a central component requires to increase
"maxClientCnxns".
Since the ZooKeeper class is expected to grow
significantly (ZooKeeper is becoming a central part
of Zuul) a split of the ZooKeeper class (zk.py) into
zk module is done here to avoid the current god-class.
Also the zookeeper log is copied to the "zuul_output_dir".
Change-Id: I714c06052b5e17269a6964892ad53b48cf65db19
Story: 2007192
d518e56208