Quieting logster::job cron

logtail2 is run by logster and spits out a message when a file doesn't
exist.  We don't need to know this, since logster properly logs to its
own log file on run (/var/log/logster/logster.log), and does the right
thing when a file doesn't exist.

Change-Id: I08cceecdc802b42345093c30e1a43606e5b24e0e