ci: try adding slc6 image

.gitlab-ci.yml

@@ -2,6 +2,22 @@ stages:
 - build
 - publish
 
+slc6:
+  stage: build
+  image: gitlab-registry.cern.ch/linuxsupport/slc6-base
+  script:
+  - yum install -y rpm-build git
+  - git fetch --tags
+  - git submodule update --recursive --init
+  - git tag
+  - git describe --dirty
+  - ./make-rpm.sh
+  - mkdir ${CI_JOB_NAME}
+  - cp -r /root/rpmbuild/RPMS build/SRPMS ${CI_JOB_NAME}
+  artifacts:
+    paths:
+    - "$CI_JOB_NAME"
+
 cc7:
   stage: build
   image: gitlab-registry.cern.ch/linuxsupport/cc7-base