Allowing to switch off ZookeeperServiceWatch

[messi612]

Is your feature request related to a problem? Please describe.
ZookeeperServiceWatch create a treecache to iterate watch /services dir, when service and service instance num increase high，the watcher num will increase dramatically as instances watch the path each other
e.g. service num is 500, instance num is 2500, the watch number will be (500 + 2500) * 2500 * 2= 15m ,multiply 2 as
path data and path children will be both watched

Describe the solution you'd like
add a swtich to disable ZookeeperServiceWatch