Extend SetHeader Requests method ito accept multiple values
Extend SetHeader Requests method ito accept multiple values

This allows to set headers that are multivalued directly.
The headers variable is not directly accessible and currently
SetHeaders allows to set only one value.

Signed-off-by: Simo Sorce <simo@redhat.com>

Kubernetes-commit: 1f44ccd01c9cea7870a4018b29fa8eabe58a90f6

caesarxuchao/client-go,kubernetes/client-go,caesarxuchao/client-go,li-ang/client-go