Adapt rake ci:migrate to accept updated 'final export' archives

The changes proposed in gitlab-org/gitlab-ci#315 will produce a new kind of export archive that we need to be able to import into GitLab 8.0 with rake ci:migrate.

Part of the CI migration improvement plan in gitlab-org/gitlab-ce#2563.

mentioned in issue #2563 (closed)

@jacobvosmaer what is the status of this issue? The linked issues are closed.

@JobV thanks for checking, yes this was done.

Status changed to closed

mentioned in merge request !14785