Allocates a new Jenkins agent using a specified Docker image and runs tasks on it. Example:

dockerNode('cloudbees/jnlp-slave-with-java-build-tools') {
    git 'https://github.com/jglick/simple-maven-project-with-tests'
    sh 'mvn -B -Dmaven.test.failure.ignore install'
    junit '**/target/surefire-reports/TEST-*.xml'
}