Make wait_for_* methods fail-fast by default

[voodam]

Problem:

We have several wait_for_* methods that by default return bool value (timeout was exceeded or not). The proper usage of this methods usualy is like this:

self.assertTrue(nginx.wait_for_connections())

Here we have problems when we forgot self.assertTrue - it can lead to hard to detect bugs (now some part of invocations of this methods haven't assert).

Proposal:

Introduce strict parameter, and check the timeout inside the method by default:

    def wait_for_connection_close(self, timeout=5, strict=True):
        """
        Try to use strict mode whenever it's possible
        to prevent tests from hard to detect errors.
        """
        timeout = adjust_timeout_for_tcp_segmentation(timeout)
        timeout_not_exceeded = util.wait_until(
            lambda: not self.connection_is_closed(),
            timeout,
            abort_cond=lambda: self.state != stateful.STATE_STARTED,
        )
        if strict:
            assert (
                timeout_not_exceeded != False
            ), f"Timeout exceeded while waiting connection close: {timeout}"
        return timeout_not_exceeded

Now we have this implemented in BaseDeproxyClient, but we should implement this in all related wait_for_* methods and switch default strict value to True (after refactoring all affected tests).