Make all future skipped builds as processable when retrying a build

What does this MR do?

Makes a builds that are marked as skipped when a pipeline is processed to be reprocessed by changing their's state to created.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Currently retry is broken. When you retry a build of pipeline it will succeed and be marked as succeeded, when the next stages should be triggered.

What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/21066

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together