Add value to add() call when locking

When BagOStuff::lock() was called, it called $this->add() with only
two parameters, the key and the timeout. But BagOStuff::add() takes
three parameters (key, value, timeout), so all locks got an infinite
timeout.

Change-Id: I82bed11b0b799f2cda13a8a0bd0cd94908b6ce8e