Trigger builds on CI instead of using webhooks

Remove prod webhook on https://gitlab.cern.ch/linuxsupport/websites/linux.cern.ch/hooks once merged

This will also avoid the pain of building feature branches and deploying it to https://linux-qa.web.cern.ch (no need to reconfigure hooks, nor to trigger builds manually).

.gitlab-ci.yml

 stages:
   - build
 
-mkdocs_test_build:
+.prod_variables: &prod_variables
+  OC_OPTIONS: --token ${LINUXWEB_PROD_OPENSHIFT} --server https://openshift.cern.ch --namespace linux
+
+.dev_variables: &dev_variables
+  OC_OPTIONS: --token ${LINUXWEB_QA_OPENSHIFT} --server https://openshift.cern.ch --namespace linux-qa
+
+.common_functions: &common_functions |
+  # redefine oc to use the appropriate options. alias doesn't work here: https://askubuntu.com/a/98786
+  function oc {
+    /bin/oc $OC_OPTIONS "$@"
+  }
+
+.common_script: &common_script |
+  oc start-build linux-docs --wait
+  
+build_test:
+  stage: build
+  image: gitlab-registry.cern.ch/paas-tools/openshift-client
+  before_script:
+    - *common_functions
+  script:
+    # We need to alter buildConfig to point to the branch (CI_COMMIT_REF_NAME) reference this CI is triggering from
+    # Use double quotes so variable interpolation works, but this requires scaping JSON patch
+    - oc patch buildconfig linux-docs -p "{\"spec\":{\"source\":{\"git\":{\"ref\":\"$CI_COMMIT_REF_NAME\"}}}}"
+    - *common_script
+  except:
+    - master
+  variables:
+    <<: *dev_variables
+
+build_prod:
   stage: build
-  image: gitlab-registry.cern.ch/authoring/documentation/s2i-mkdocs-container:1.1
+  image: gitlab-registry.cern.ch/paas-tools/openshift-client
   before_script:
-    - export LC_ALL=en_US.utf-8
-    - export LANG=en_US.utf-8
+    - *common_functions
   script:
-    - export PYTHONPATH=$PYTHONPATH:/opt/app-root/lib/python3.6/site-packages
-    - /opt/rh/rh-python36/root/bin/pip install --cache-dir /opt/app-root/.cache --target /opt/app-root/lib/python3.6/site-packages -r requirements.txt
-    - /opt/rh/rh-python36/root/bin/mkdocs build
-  artifacts:
-    paths:
-      - site
-    expire_in: 1 week
+    - *common_script
+  variables:
+    <<: *prod_variables
+  only:
+    - master