Add the 'backup' tag to enble quickstack for 7
Add the 'backup' tag to enble quickstack for 7

This patch adds the 'backup' tag that is needed for the quickstart
image creating playbook.
Without it, the quickstart image is created with the TTY problem we
already fixed as it was not running as part of the run

Change-Id: I7e9cbdf86c4b32d3f237d2d8f8e509aedf1bcbb5

okolisny/InfraRed,okolisny/InfraRed,redhat-openstack/infrared,redhat-openstack/infrared,okolisny/InfraRed,redhat-openstack/infrared