title: Jenkins cannot launch docker slave using docker plugin
body: <p>I am using Jenkins Docker plugin to launch slaves dynamically on the docker host. Jenkins master runs on the same host. When building, it picks a random port on the docker-host and cannot connect to it. It launches docker containers. Here are the logs. Doesn't say more than this.  How to debug the issue? </p>
  
  <pre><code>INFO: Started container ID 54fe5780ca820a6e2b7cae40610cfc3229dbf889b0c66d6e34a39b74e13aaec7 for node slave-0000w16w841rc from image: jenkinsubuntu
  Feb 28, 2019 9:35:54 PM com.nirima.jenkins.plugins.docker.utils.PortUtils$ConnectionCheckSSH execute
  INFO: SSH port is open on 127.0.0.1:10007
  [02/28/19 21:35:54] SSH Launch of slave-0000w16w841rc on 127.0.0.1 failed in 29 ms 
  Feb 28, 2019 9:36:03 PM hudson.slaves.NodeProvisioner$2 run
  INFO: Image of jenkinsubuntu provisioning successfully completed. We have now 7 computer(s) `
  </code></pre>