RFR: git-webrev: add support for "upstream" remote

[Robin Westberg]

On Mon, 9 Dec 2019 14:37:31 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this small patch that add supports to `git-webrev` for repositories with a remote named `upstream` (used for discovering the upstream repository).
> 
> Thanks,
> Erik
> 
> ## Testing
> - [x] Manual testing of `git-webrev`

Looks good!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/303