Use prebuilt images for ohpc,ood,compute nodes

vars.tf

@@ -34,18 +34,18 @@ variable "internal-subnet" {
 }
 
 variable "image_ohpc" {
-  default = "CentOS-7-x86_64-GenericCloud-1905"
+  default = "ohpc-V0.4"
 }
 
 variable "image_ood" {
-  default = "CentOS-7-x86_64-GenericCloud-1905"
+  default = "ood_1"
 }
 
 variable "image_compute" {
-  default = "CentOS-7-x86_64-GenericCloud-1905"
+  default = "compute"
 }
 variable "compute_node_count" {
-  default = 2
+  default = 1
 }
 
 variable "keypair-name" {