`getIsPortTaken` does not work and break the `usedPortAction` option

[nrako]

This following method getIsPortTaken might falsely return false, even though a server might be running on the configured protocol, host and port.

jest-process-manager/src/index.ts

Lines 121 to 134 in ff7018a

	function getIsPortTaken(config: JestProcessManagerOptions) {
	let server: net.Server
	const cleanupAndReturn: (val: boolean) => void = result =>
	new Promise(resolve => server.once('close', () => resolve(result)).close())
	return new Promise((resolve, reject) => {
	server = net
	.createServer()
	.once('error', (err: JestProcessManagerError) =>
	err.code === 'EADDRINUSE' ? resolve(cleanupAndReturn(true)) : reject(),
	)
	.once('listening', () => resolve(cleanupAndReturn(false)))
	.listen(config.port, config.host)
	})
	}

This renders usedPortAction useless, and for example would lead to a server being started while ignore should have prevented that.

From what I understood this is because of SO_REUSEADDR and SO_REUSEPORT:

Package such as node-portscanner would use net.Socket() to prevent that: https://github.com/baalexander/node-portscanner/blob/4fc93fe2a5cc9db983caab57bfe27cbee4de9cc5/lib/portscanner.js#L100-L135

[mmarkelov]

@nrako thanks for report! I'll try to investigate this soon