Bug#730167: atop: Atop cron error: invoke-rc.d: action _cron is unknown, but proceeding anyway

[Marti Raudsepp]

Also reported to Ubuntu: https://bugs.launchpad.net/dabo/+bug/1290271

The solution is simple: just change the invoke-rc.d call to use --quiet to
suppress the error.

Regards,
Marti