Add a presubmit job for windows on GCE
Add a presubmit job for windows on GCE

The change also factor out common environment variable for Windows test
jobs.

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