The default handler now uses contextual logging. Instead of
warnings.go:106] warning 1
it now logs the caller of client-go and uses structured, contextual
logging
main.go:100] "Warning" message="warning 1"
Users of client-go have the choice whether the handler that they provide uses
the traditional API (no API break!) or contextual logging.
Kubernetes-commit: 48fb886325fce4b16e4067caadb7bcd3044d460f
