bump CUDA builder disk size (build ran out of space)

Author: sjpb

packer/openstack.pkr.hcl

@@ -129,7 +129,7 @@ variable "volume_size" {
     # fat image builds, GB:
     openhpc = 15
     openhpc-ofed = 15
-    openhpc-cuda = 25
+    openhpc-cuda = 30
   }
 }