The problem was in a test case for Bug33507:
  - when the number of active connections reaches the limit,
    the server accepts only root connections. That's achieved by
    accepting a connection, negotiating with the client and
    checking user credentials. If it is not SUPER, the connection
    is dropped.
  - when the server accepts connection, it increases the counter;
  - when the server drops connection, it decreases the counter;
  - the race was in between of decreasing the counter and accepting
    new connection:
    - max_user_connections = 2;
    - 2 oridinary user connections accepted;
    - extra user connection is establishing;
    - server checked user credentials, and sent 'Too many connections'
      error;
    - the client receives the error and establishes extra SUPER user
      connection;
    - the server however didn't decrease the counter (the extra
      user connection still is "alive" in the server) -- so, the new
      SUPER-user connection, will be dropped, because it exceeds
      (max_user_connections + 1).

The fix is to implement "safe connect", which makes several attempts
to connect and use it in the test script.


mysql-test/r/connect.result:
  Update test file.
mysql-test/t/connect.test:
  Avoid races in connect.test.
mysql-test/include/connect2.inc:
  Auxiliary routine to establish a connection reliably.