Implement a test to ensure that cluster properly interoperates with the --{inspect,debug}-brk options

When started with any of the --inspect* or --debug* options, the cluster module is supposed to provide a unique port to the child processes. The existing test for this functionality seems to lack ability to test the --inspect-brk and --debug-brk flags.

It would be good to add a test (or modify the existing test) to be add this capability.

See: #11386 (comment).