Add test fixture for Apigee PAYG Env Node Config

Added test fixture for Apigee PAYG Environment
Node Config.

Changes committed:
- modified:   `tests/modules/apigee/fixture/test.env_only.tfvars`

tests/modules/apigee/fixture/test.env_only.tfvars

@@ -4,5 +4,9 @@ environments = {
     display_name = "APIs test"
     description  = "APIs Test"
     envgroups    = ["test"]
+    node_config = {
+      min_node_count = 2
+      max_node_count = 5
+    }
   }
 }