Cleanup CI variables table and add a deprecation note (!9831) · Merge requests · GitLab.org / GitLab FOSS · GitLab

Achilleas Pipinellis - OOO until November 25th (parental leave) requested to merge docs/ci-variables-deprecation-table into master Mar 09, 2017

Addresses discussion starting from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9756#note_25041251