Bump image size to 16 GiB

This is necessary due to the additional OOD apps.

Author: priteau

packer/openstack.pkr.hcl

@@ -125,7 +125,7 @@ variable "volume_type" {
 
 variable "volume_size" {
   type = number
-  default = 15
+  default = 16
 }
 
 variable "image_disk_format" {