Add test config for GCE GPU stable2-stable1 upgrade test.
Add test config for GCE GPU stable2-stable1 upgrade test.

GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid