Update centos 6 image to 6.9
Created by: doublej472
This updates CentOS 6 to the 6.9 version and fixes an issue I had with setting QEMU memory usage.
As a side note, I was unable to create a branch on this repository, I had to fork it in order to push changes.
ERROR: Permission to osuosl/packer-templates.git denied to doublej472.