Add EE fixtures to SeedFu fixture paths
As per https://github.com/mbleigh/seed-fu#where-to-put-seed-files, the default paths which SeedFu looks for fixtures in are #{Rails.root}/db/fixtures
and #{Rails.root}/db/fixtures/#{Rails.env}
. With https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/11244, we now have an EE-only fixture to import a license automatically during db seeding.
This MR adds EE db fixture paths to the places where SeedFu looks for fixtures.