call saveToFile OnStop
call saveToFile OnStop

This is better than waiting because while we wait, anything could happen
(crash, timeout of the code who's using addrbook, ...). If we save
immediately, we have much greater chances of success.

tendermint/go-p2p,tendermint/tendermint,tendermint/tendermint,tendermint/tendermint,tendermint/tendermint