Add interpretPatchError to return appropriate http code
(400 or 422) according to the error type.
We add this function in apiserver because we don't want
to mention the http code in apimachinery. The apimachinery
code is also used in kubectl. The client should not return
a server error.
Add a test to validate the http error code and error message.
Kubernetes-commit: e0a2168ecbf8b4e43f932a32fa55cd55215123cc
Nikhita Raghunath