The problem is that the read and write methods of the shared
memory transport (protocol) didn't react to asynchronous close
events, which could lead to a lock up as the client would wait
(until time out) for a server response that will never come.

The solution is to also wait for close events while waiting
for I/O from or to the server.

mysql-test/r/shm.result:
  Add test case result for Bug#33899
mysql-test/t/shm.test:
  Add test case for Bug#33899
vio/viosocket.c:
  Also wait for close events.