Resolve periodic socket.timeout causing control channel socket recycling

[MaicoTimmerman]

For every message send from the Enterprise Gateway to the kernel, a new connection is accepted using socket.accept(). The timeout for this socket is 5 seconds:

enterprise_gateway/etc/kernel-launchers/python/scripts/launch_ipykernel.py

Line 293 in d01e84a

sock.settimeout(5)

Instead of restarting the blocking accept call, we can use select.select to check ready-state of the socket. Using this method we don't cycle the connection and delay (or miss) messages.