[Jenkins] Push docker images.

Jenkinsfile

 #!/usr/bin/env groovy
 @Library('jenkins-pipeline@1.0.9') _
 
-def stage_required = [build: false, data: false, full: false]
+def stage_required = [build: false, data: false, full: false, docker: false]
 
 pipeline {
   agent none
@@ -55,6 +55,10 @@ pipeline {
                   stage_required.data = true
                   echo "Updating Tests/Data."
                 }
+                if (path.startsWith("scripts/docker") && !stage_required.docker) {
+                  stage_required.docker = true
+                  echo "Doing Docker images build."
+                }
               }
             }
           }
@@ -335,6 +339,26 @@ pipeline {
     stage('Master') {
       when { environment name: 'JOB_NAME', value: 'ufz/ogs/master' }
       parallel {
+        // ********************* Push Docker Images ****************************
+        stage('Push Docker Images') {
+          when {
+            beforeAgent true
+            expression { return stage_required.docker || stage_required.full }
+          }
+          agent { label 'docker' }
+          steps {
+            script {
+              dir('scripts/docker') {
+                def gccImage = docker.build("ogs6/gcc:latest", "-f Dockerfile.gcc.full .")
+                def clangImage = docker.build("ogs6/clang:latest", "-f Dockerfile.clang.full .")
+                docker.withRegistry('https://registry.hub.docker.com', 'docker-hub-credentials') {
+                  gccImage.push()
+                  clangImage.push()
+                }
+              }
+            }
+          }
+        }
         // ************************* Analyzers *********************************
         stage('Analyzers') {
           when {

web/content/docs/devguide/advanced/docker.pandoc

@@ -81,3 +81,9 @@ make ogs
 ./bin/ogs
 ```
 
+## OGS-6 images used by Jenkins
+
+The following images are used by Jenkins:
+
+- `ogs6/gcc`, defined in [scripts/docker/Dockerfile.gcc.full](https://github.com/ufz/ogs/blob/master/scripts/docker/Dockerfile.gcc.full)
+- `ogs6/clang`, defined in [scripts/docker/Dockerfile.clang.full](scripts/docker/Dockerfile.clang.full)