Artifacts are in the middle of being migrated from ci_builds to
ci_job_artifacts. The expiration date is currently visible in both of
these tables and the test for whether an expired artifact is present
for a job is complex as it requires checking both the of the tables.

Add two new indexes, one on ci_builds.artifacts_expire_at and one on
ci_job_artifacts.expire_at to enable finding expired artifacts
efficiently.

And until the migration is finished, replace the SQL for finding
expired and non-expired artifacts with a hand-crafted UNION ALL based
query instead of using OR. This overcomes a database optimizer
limitation that prevents it from using these indexes.

When the migration is finished the next version should remove this
query and replace it with a much simpler query on just
ci_job_artifacts. See
https://gitlab.com/gitlab-org/gitlab-ce/issues/42561 for followup.

I've followed the [upgrade guide](https://github.com/thoughtbot/factory_bot/blob/4-9-0-stable/UPGRADE_FROM_FACTORY_GIRL.md

) and ran these two commands:

```
grep -e FactoryGirl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|FactoryGirl|FactoryBot|"
grep -e factory_girl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|factory_girl|factory_bot|"
```

Signed-off-by: Rémy Coutable <remy@rymai.me>

Two things at ones, as there was no clean way to seperate the commit and
give me feedback from the tests.

But the model Artifact is now JobArtifact, and the table does not have a
type anymore, but the metadata is now its own model:
Ci::JobArtifactMetadata.

To allow jobs/builds to have multiple artifacts, and to start seperating
concerns from Ci::Build a new model is created: Ci::Artifact.

Changes include the updating of the ArtifactUploader to adapt to a
slightly different interface. The uploader expects to be initialized
with a `Ci::Build`.

Futher a migration with the minimal fields, the needed foreign keys and
an index.

Last, the way this works is by prepending a module to Ci::Build so we
can basically override behaviour but if needed use `super` to get the
original behaviour.

Minor annoyance of mine, and there were a couple of things wrong, for
example:
1. Switching on a property is just a trait
2. It didn't inherrit from its parent

Find and replace through the code based fixed all occurances.

Squashed commit of the following:

commit 43e5bba774e9e383dd55c665e82f6fcfc4ebfc4f
Author: Shinya Maeda <gitlab.shinyamaeda@gmail.com>
Date:   Mon Apr 17 17:28:44 2017 +0900

    Add fix

commit 09610eebdf22ad048812bb86022504b2ad917e19
Author: Shinya Maeda <gitlab.shinyamaeda@gmail.com>
Date:   Mon Apr 17 17:03:49 2017 +0900

    Add trace test

Adds tests