Fix creation of Ci::Commit object which can lead to pending, failed in some scenarios

## What does this MR do?

If we use a new `project.ci_commits` it will add it to array, and some other services which can do a save on a project can lead to a scenario when `ci_commit` will be saved, where it should not be.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-com/support-forum/issues/717 https://gitlab.com/gitlab-com/support-forum/issues/715 https://gitlab.com/gitlab-org/gitlab-ce/issues/17596 https://gitlab.com/gitlab-com/support-forum/issues/714 https://gitlab.com/gitlab-org/gitlab-ce/issues/13402

cc @rymai 


See merge request !4214