Add build, verify, test-go, and kubelet jobs for release-1.6.
Add build, verify, test-go, and kubelet jobs for release-1.6.

Also reduce frequency of kubernetes-verify-release-1.3

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