build/kubernetes: add secret API methods

- add Get and Create secret
- refactor client
- fix example

Change-Id: Ia5c6f17e86cb01aa8093ec058630b40ee61fa74f
Reviewed-on: https://go-review.googlesource.com/21765
Reviewed-by: Evan Brown <evanbrown@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2 files changed