test new build agent

Dockerfile

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+FROM docker.io/jenkins/jenkins:lts
+
+USER root
+RUN apt-get update && apt-get install -y --no-install-recommends mercurial
+
+USER jenkins

Jenkinsfile

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+pipeline {
+    agent none
+    environment {
+        CHAT = "spacenerdmo@clacks.network"
+    }
+    stages {
+        stage('Build docker image') {
+            agent { label 'testbuilder' }
+            environment {
+                TAG = "lts"
+            }
+            steps {
+                jabberNotify buildToChatNotifier: [$class: 'ExtraMessageOnlyBuildToChatNotifier'], extraMessage: 'Build Started', notifySuspects: true, targets: "${CHAT}"
+                script {
+                    docker.withRegistry('https://git.dreamfall.space/thrrgilag', 'thrrgilag-forgejo-pkg') {
+                        def customImage = docker.build("git.dreamfall.space/thrrgilag/jenkins-mercurial:${TAG}")
+                        customImage.push()
+                    }
+                }
+            }
+            post {
+                success {
+                    jabberNotify buildToChatNotifier: [$class: 'ExtraMessageOnlyBuildToChatNotifier'], extraMessage: 'Build Succeeded', notifySuspects: true, targets: "${CHAT}"
+                }
+                failure {
+                    jabberNotify buildToChatNotifier: [$class: 'ExtraMessageOnlyBuildToChatNotifier'], extraMessage: 'Build Failed', notifySuspects: true, targets: "${CHAT}"
+                }
+            }
+        }
+    }
+}