The args passed to Mgr.CreateService end up as the command-line
arguments (available via os.Args), not as the args passed to
Svc.Handler.Execute.

Fixes golang/go#20440

Change-Id: I55a1ec3432b377082c018fe960114c96350e8978
Reviewed-on: https://go-review.googlesource.com/43714Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>