review: modify argument parsing for use as a git sub-command

For this command to be invoked as "git change", "git upload", etc
we must parse the -v and -n arguments after the command name.

Change-Id: I4beb386379457c7a49910bd0b7ee4fd8aa5cc609
Reviewed-on: https://go-review.googlesource.com/1120
Reviewed-by: Andrew Gerrand <adg@golang.org>