`bitcoind` can take a long time to flush its db cache to disk upon
shutdown. Most init files send a `SIGKILL` after a timeout of 1 minute,
causing unclean shutdowns and triggering a long "Rolling forward" at the
next startup. Increasing this timeout to 10 minutes should reduce how
often this occurs, especially during IBD.
fixup! Set ProtectHome in systemd service file
This allows users to specify, e.g. raise, the default timeout of 60
seconds. Some bitcoind instances, especially long running ones on slow
hardware, require a higher timeout for a clean shut down.
Also add a comment to bitcoind.openrc's 'retry=', since it is not
obvious from the variable name what it does.
