CI: use docker image from XLAB nexus repo

.gitlab-ci.yml

-image: docker:stable
+image: nexus-registry.xlab.si:5001/docker:stable
 
 variables:
   REGISTRY: registry-gitlab.xlab.si
@@ -11,6 +11,8 @@ stages:
 - deploy
 
 before_script:
+- mkdir -p $HOME/.docker
+- echo "$DOCKER_AUTH_CONFIG" > $HOME/.docker/config.json
 - export SERVICE=cce-frontend
 - export VERSION=$(grep -w "version" package.json | cut -d ':' -f 2 | cut -d ',' -f 1 | xargs echo)