fix(server): Force clients disconnect on Windows

It occurs that only on Windows, socket.io clients are not properly disconnected, which causes Karma to not exit immediately when everything is done. We have to wait for some internal disconnection socket.io event timeout.

This PR basically check if all sockets are disconnected. If not we manually force the disconnection.

Fixes #1109
Merge branch 'pr-1121' into presubmit-master-pr-1121