Use an 11 second download in sbws

In legacy/trac#22453 (moved), we might remove relay bandwidth self-tests in Tor. So we want sbws to send bandwidth for Tor's entire 10 second bandwidth interval.

Let's set the download_target to 11 seconds (to cover the 10 second interval), and adjust the min to 7 and the max to 14?

Version sbws 1.0.0