Move kubemark-1.5 job to 1.8 (last release)
Move kubemark-1.5 job to 1.8 (last release)

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