cmd/coordinator/buildongce: fix tests

Fixes golang/go#26476

Change-Id: I380e47cfc0d51d0c297a2d7e5cdb263e09bcfd9c
Reviewed-on: https://go-review.googlesource.com/124975
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: Robert-André Mauchin

cmd/coordinator/buildongce/create_test.go

@@ -30,7 +30,7 @@ resources:
       logging_service: "logging.googleapis.com"
       monitoring_service: "none"
       node_config:
-        machine_type: "n1-standard-8"
+        machine_type: "n1-standard-4"
         oauth_scopes:
           - "https://www.googleapis.com/auth/cloud-platform"
           - "https://www.googleapis.com/auth/userinfo.email"