#31 adds pre-check before starting TCP/HTTP executor

that overwriting is tricky, because you might get unsuccessful head, but port might be already taken.

So, it would make sense, to check HEAD on http level, but as we go deeper through start methods, on TCP it makes sense to check TCP start_check.

This made me thinking, that in case, when we determine, that HEAD was unsuccessful, so we can start executor, and we try to start it, but TCP is taken - can we get same error, where we try to terminate executor due to unsuccessful head, but it stopped itself, because it couldn't bind with port?