Minor clean-ups in VMInstall and its type implementations

[HannesWell]

What it does

Clean-up the code in VMInstall and VMInstallType implementations in order to simplify it.

Author checklist

• [ ] I have thoroughly tested my changes
• [x] The change is following the coding conventions
• [x] I have signed the Eclipse Contributor Agreement (ECA)

[HannesWell]

Thanks for your review.