Automatic merge from submit-queue
add wrapper to provide stderr on command errors
The go standard library doesn't include stderr in the error message, but in many cases it is present: https://golang.org/src/os/exec/exec.go#L389 . This adds a wrapper to display that information. I've added in it on spot where the kops test is having trouble. If it works well, we can add it elsewhere.
@wojtek-t ptal
7d611fe32b