Specify where VM images are coming from across GCE projects (#7985)

automerge

net/scripts/gce-provider.sh

@@ -174,7 +174,7 @@ cloud_CreateInstances() {
     # the stock Ubuntu 18.04 image and programmatically install CUDA after the
     # instance boots
     #
-    imageName="ubuntu-1804-bionic-v20181029-with-cuda-10-and-cuda-9-2"
+    imageName="ubuntu-1804-bionic-v20181029-with-cuda-10-and-cuda-9-2 --image-project principal-lane-200702"
   else
     # Upstream Ubuntu 18.04 LTS image
     imageName="ubuntu-1804-bionic-v20190813a --image-project ubuntu-os-cloud"