Add test for kops on centos7
Add test for kops on centos7

There was an issue installing docker on centos7, so we want it under
e2e.

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