test: race condition in test-cluster-disconnect
test: race condition in test-cluster-disconnect

The test was not waiting for all the worker-created sockets
to be listening before calling cluster.disconnect().
As a result, the channels with the workers could get closed
before all the socket handles had been passed to them, leading
to various errors.

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node