Add diff command return status code greater than 1 when flags invalid
Add diff command return status code greater than 1 when flags invalid

This PR adds flagerror handler function to detect when flags are invalid.
Default flag handler returns status code 1. However, diff command embraces
this status code as changes are found. By overriding flag errors,
this PR shows same message with default case and returns status code 2.

Kubernetes-commit: 4f0848520d4cdd679c76479949546002c5935e3c

kubernetes/kubectl,kubernetes/kubectl