Configure VCS drivers list

We installed and set up GitLab and Packagist, added private repository from GitLab into our Packagist; everything works fine, except one moment: package's "dist" value is always null and composer.phar is not able to download package as zip-file from GitLab.

This changes will allow to add VCS-driver to Packagist instance via composer's global config file and to have not-null "dist" values for private repositories.