integ: hold kit fake keep-alive sockets past aiohttp's reuse window

Every kit fake closed an idle keep-alive socket at node's 5s default while
the python host's aiohttp pool reuses one for up to 15s and never reads the
advertised timeout. A request written at the closing instant is answered
with a disconnect, and aiohttp re-sends only an idempotent method; dropbox
posts every read, so grep -rl died on main with 'Server disconnected'.
Set keepAliveTimeout to 60s in createKitServer and pin it in the kit
selftest by reading the Keep-Alive header off the wire.