update-notifier upstart job should be silent by default

I happened to be looking in my ~/.cache/upstart directory, and noticed that I had quite a few logs from update-notifier-crash.

$ ls ~/.cache/upstart/update-notifier-crash-_var_crash_* | wc -w
477
$

These logs get rotated, but are never expired out for old crashes if there's no new log... so you wind up with a large number of log files here, at least one for each application that has ever crashed. I think we should avoid this by being silent by default. If we need to log activity, perhaps we should use logger instead to send these messages to syslog.

Example log output:

Mon Feb 24 21:53:23 PST 2014 crash report /var/crash/linux-image-3.13.0-8-generic.257633.crash detected

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: update-notifier 0.154.1
ProcVersionSignature: Ubuntu 3.13.0-19.40-generic 3.13.6
Uname: Linux 3.13.0-19-generic x86_64
ApportVersion: 2.14.1-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Apr 11 10:25:04 2014
InstallationDate: Installed on 2010-09-24 (1295 days ago)
InstallationMedia: Ubuntu 10.04.1 LTS "Lucid Lynx" - Release amd64 (20100816.1)
SourcePackage: update-notifier
UpgradeStatus: Upgraded to trusty on 2013-10-23 (170 days ago)
upstart.update-notifier-cds.log:
 Thu Apr 10 23:13:46 PDT 2014 CD found at /dev/sdd
 CD mounted at
upstart.update-notifier-release.log:
 Wed Apr 9 22:24:07 PDT 2014 new release available
 Wed Apr 9 22:24:08 PDT 2014 new release available
 Wed Apr 9 22:25:37 PDT 2014 new release available