Change back to generic image description now that GCE is fixed.
Update default image used for Azure.

Fixes CVE-2014-6271.
Still vulnerable to CVE-2014-7169.
Merge pull request #1493 from MSOpenTech/azure-image

Update default image used for Azure.
Merge pull request #1492 from jbeda/backports-fix

Change back to generic image description now that GCE is fixed.