[Yum] RFE "quiet" mode

[garrick]

I'm now using yum to support my RH linux cluster, and it's working
great.  Yum is being run from cron jobs that makes sure all nodes are in
sync.  I just need one small thing: less verboseness.  When cron sends
a daily email with the output of nearly 600 machines, it's impossible to
quickly glance for errors.  I was thinking maybe -q could suppress all
normal output; only printing error messages.