test: dynamic port in cluster worker disconnect

Remove common.PORT from test-cluster-worker-disconnect-on-error
possibility that a dynamic port used in another test will collide
with common.PORT.

PR-URL: https://github.com/nodejs/node/pull/12457
Ref: https://github.com/nodejs/node/issues/12376


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>