Do not wait until wsReader routine gracefully finishes its work before
WS connection close. Instead, firstly close the connection, and after
that wait for proper wsReader exit.
It's a harsh way, but I don't have any other options to try, because
wsReader routine hangs on `ws.ReadMessage()` operation for more than
ReadDeadline (more than 5 seconds) during test cleanup which results in
the test timeout.
Close#3378.
Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>