Connector spams timeout error when polling

[drewdzzz]

Functions like wait and waitAny are the only way to poll connections to Tarantool. The problem is they log errors on timeout, so polling actually pollutes output with these warnings. We should do something about it, possible variants:

1. Simply drop the warnings - not really great since one can use wait to synchronously wait for a request, in this case the warning would be handy.
2. Add a new argument to notify the connector that wait is used for polling. Solves the problem, but not really convenient.
3. Add a new function poll that is actually the same as wait but without warning.