Improve windows support for git-review --setup

If git-review is not run in git repo top-level dir, then the target
path used for scp uses both "/" and "\", and scp fails.

Change-Id: I8ffe163f9e29423b1c19bd54241a526a9843561f
Closes-Bug: #1024073
Merge "Improve windows support for git-review --setup"