choice of idleswap times, it was sending the email before the expt had
even been idle for 5 minutes. So add a check to make sure that they're
idle at least idle_threshold minutes before we send warnings. Meaning, if
the swap time is 30 minutes, and the warning time is 30 minutes, you won't
get a warning at all, instead of warnings every time you've been idle for
1 minute (ie it has been a minute since the last node reported activity).