This commit fixes a bug where the cluster module fails to propagate
EADDRINUSE errors.
When a worker starts a (net, http) server, it requests the listen socket
from its master who then creates and binds the socket.
Now, OS X and Windows don't always signal EADDRINUSE from bind() but
instead defer the error until a later syscall. libuv mimics this
behaviour to provide consistent behaviour across platforms but that
means the worker could end up with a socket that is not actually bound
to the requested addresss.
That's why the worker now checks if the socket is bound, raising
EADDRINUSE if that's not the case.
Fixes#2721.
This test starts two clustered HTTP servers on the same port.
It expects the first cluster to succeed and the second cluster
to fail with EADDRINUSE.
Reapplies commit cacd3ae, accidentally reverted in a2851b6.
uncaughtException handlers installed by the user override the default one that
the cluster module installs, the one that kills off the master process.
Fixes#2556.