Replace staging flag cloud-print-service with cloud-print-url.

Replace obsolete '--cloud-print-service=https://cloudprint.sandbox.google.com/cloudprint'
with new '--cloud-print-url=https://cloudprint-nightly-ps.sandbox.google.com/cloudprint'
(changed per CL 204050)

BUG=None
TEST=Run on a test image.

Change-Id: Ief4fa69304938da91dada0b3901a8d1b28e170a8
Reviewed-on: https://chromium-review.googlesource.com/250620
Tested-by: Scott Cunningham <scunningham@chromium.org>
Reviewed-by: Kris Rambish <krisr@chromium.org>
Reviewed-by: Scott Cunningham <scunningham@chromium.org>
Commit-Queue: Scott Cunningham <scunningham@chromium.org>
diff --git a/provingground/mod_test_image_for_staging.sh b/provingground/mod_test_image_for_staging.sh
index 1defaac..8c18825 100755
--- a/provingground/mod_test_image_for_staging.sh
+++ b/provingground/mod_test_image_for_staging.sh
@@ -69,7 +69,7 @@
 --google-apis-host=www-googleapis-test.sandbox.google.com
 --oauth2-client-id=236834563817.apps.googleusercontent.com
 --oauth2-client-secret=RsKv5AwFKSzNgE0yjnurkPVI
---cloud-print-service=https://cloudprint.sandbox.google.com/cloudprint
+--cloud-print-url=https://cloudprint-nightly-ps.sandbox.google.com/cloudprint
 --ignore-urlfetcher-cert-requests
 
 # mod_test_image_for_staging.sh modifications end here.