Git.push only works with remote "origin"

[schnatterer]

When implementing Git.pull() we wondered why Git.push() is implemented as git push origin ${refSpec}. With this it is impossible to push to other remotes than origin.

It would be a good idea to remove the origin, but then this would break backwards compatibility.

So with a version 2.x of ces-build-lib this behaviour should change.
For now, we implement pull() without origin so it behaves more correct but different than push() :-/