Improve JNLP Port Unreachable error message with host value

[Dohbedoh]

Propose a quick improvement to display the host that is actually used to test that the JNLP port is unreachable. That message is often misleading because it is showing the Jenkins URL.

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue