chat tests: Give some time to process each of the 140 chat messages
chat tests: Give some time to process each of the 140 chat messages

This avoids overflowing socket.io's receive buffer.

ether/etherpad-lite,ether/etherpad-lite,storytouch/etherpad-lite,storytouch/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite