title: Jenkins - Can't execute stage in Docker container
body: <p>On Docker Toolbox I have pulled and started jenkins container with privilleged mode:</p>
  
  <pre><code>docker run -d --security-opt label=disable --name jenkins -p 8080:8080 -p 50000:50000 jenkins/jenkins:lts
  </code></pre>
  
  <p>I installed sugested plugins and created pipeline with following script:</p>
  
  <pre><code>pipeline {
      agent {
          docker { image 'node:7-alpine' }
      }
      stages {
          stage('Test') {
              steps {
                  sh 'node --version'
              }
          }
      }
  }
  </code></pre>
  
  <p>After build was triggered following error appeared in build console:</p>
  
  <pre><code>/var/jenkins_home/workspace/test@tmp/durable-148d5c09/script.sh: docker: not found
  </code></pre>
  
  <p>Why this error occcurs? What should I do if I want to use docker containers as agents for building stages? :)</p>
  
  <p><strong>Thanks for help!</strong></p>