Add option to used private repos in requirements

[cgrimal]

Add a dockerSshSymlink option which is a path to your .ssh folder containing your keys.
If the passphrase is empty, you will be able to package your private repos from the docker container.
Solves #69 ?

[cgrimal]

Also works with a non-empty passphrase now, by using the ssh authentication socket (thanks @dschep)!

[dschep]

Awesome! Thanks so much @cgrimal. Glad the ssh-agent solution worked too. I'll check it out and make a new release when I get home from work today.

[cgrimal]

Hi Daniel,
I'm afraid it doesn't work as expected... There is a conflict with the -u option because the pip install command is not run as root, and the ssh keys are not used. It worked when I tested it because I was running everything as root and I did not pay attention to that, my bad. 😞
I am working on a workaround though, I'm hoping to have a solution today, I'll update the pull request.
Clément