Allow running git repo commands from sub directories in the repository

[Crazybus]

This pull request allows you to use git-repo from any sub directory just like you can with the vanilla git client.

Before

❯ git hub request fetch 187
Successfully fetched request id `187` of `guyzmo/git-repo` into `requests/github/187`!
❯ cd git_repo/services
❯ git hub request fetch 187
Fatal error: Cannot find path to the repository.

After

❯ git hub request fetch 187
Successfully fetched request id `187` of `guyzmo/git-repo` into `requests/github/187`!
❯ cd git_repo/services
❯ git hub request fetch 187 
Successfully fetched request id `187` of `guyzmo/git-repo` into `requests/github/187`!

Git client behavior

❯ git status
On branch yellow_submarine
nothing to commit, working tree clean
❯ cd git_repo/services
❯ git status
On branch yellow_submarine
nothing to commit, working tree clean

[guyzmo]

Hello @Crazybus this is really awesome you did that ! ♥

I'm really snowed under by work, but I promise as soon as I get two seconds, I'll review this, as well as the gerrit PR.

[Crazybus]

@guyzmo Aren't we all :) Take your time and I hope things get a bit less hectic for you soon! I'm not in a rush since I'm using this version locally of course :P

[guyzmo]

so far, so good 👍

It's simple, it's tested, it's working! Nothing to say 😉

I'll ship that one along with the gerrit request for the next release.