Fix Issue #471

[Theoderich]

fixes #471

• Check if an instance actually exists in the cloud before trying to delete it
• Terminate jenkins nodes immediately if the isntance failed to start in the cloud

Testing done

Currently testing on self hosted jenkins in our company. Will report back with results

If any automated tests need to be changed to test this behavior, I would appreciate some help

Submitter checklist

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