Fixing license headers

[Pensu]

Currently running make check-license fails with the error:

$ make check-license
>> checking license headers
-e license header checking failed:
-e   ./test/kubetest/kubetest.go
-e   ./test/kubetest/kubernetes.go
-e   ./test/e2e/basics.go
-e   ./test/e2e/main_test.go
make: *** [check-license] Error 255

This PR adds headers to the relevant files, so license check doesn't fail.

[brancz]

Thanks! lgtm 👍

[metalmatze]

Whoops, my bad. Thanks for adding!