Use group gitlab runners

.gitlab-ci.yml

@@ -3,17 +3,14 @@ image: registry.gitlab.com/ultimaker/cura/cura-build-environment:centos7
 stages:
   - build
 
-build-and-test:
+build and test linux:
   stage: build
+  tags:
+    - cura
+    - docker
+    - linux
   script:
     - docker/build.sh
   artifacts:
     paths:
       - build
-
-build-and-test_merge-requests:
-  stage: build
-  script:
-    - docker/build.sh
-  only:
-    - merge_requests