Handle NOT_BUILT results more clearly

[mattiasbpersson]

Jenkins job that have Result NOT_BUILT are reported as errors which confuses developers.

Added new commit state UNKNOWN and handle NOT_BUILT Result with description "This commit was not built".

• [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
• [x] Ensure you have provided tests - that demonstrates feature works or fixes the issue