contint: generate .gitconfig files for all jenkins users

A .gitconfig file is required by git whenever it does commit operation.
It was previously generated by misc::contint::test::jenkins which was
only applying to the jenkins user.

This move the .gitconfig file definition from
misc::contint::test::jenkins under the role::ci::{master,slave} class
and craft .gitconfig file for the jenkins-slave user.

Change-Id: If71f4fb3dec16375ca1491ee54e8a874165c97fd
Merge "contint: generate .gitconfig files for all jenkins users" into production