Make mysql backup crons quiet.

* modules/mysql_backup/manifests/backup.pp: Ignore the mysql.event table
when dumping all databases so that cron jobs are silent and do not
output a warning that this table was not dumped.

Change-Id: I5f7065d4184ca2ecd997bfc3d1beefee47c12acb
Merge "Make mysql backup crons quiet."