Revert "gitlab-runner: Always use latest state of gitlab-runner packages"

This differs from the way we install packages in all the other roles, so
revert the commit to ensure consistency.

This reverts commit ab1d8e84.

roles/gitlab_runner/tasks/main.yml

 - name: Install dependencies
-  pacman: name=docker,python-docker,python-gitlab,gitlab-runner state=latest update_cache=yes
+  pacman: name=docker,python-docker,python-gitlab,gitlab-runner state=present
   notify: Restart gitlab-runner
 
 - name: Install docker.slice