Increase the image size for security hardened images to 23G
Increase the image size for security hardened images to 23G

In recent deployes we needed to increase size of /var volume
by 3G. So we need to give the image the right size to fit there.

Change-Id: I3885a5c359b56c515dbb9286ded1dee062cdcffc

openstack/tripleo-common,openstack/tripleo-common