Added drone service
What does this MR do?:
This MR add drone ci support as service interface
Are there points in the code the reviewer needs to double check?:
- https://gitlab.com/bugagazavr/gitlab-ce/blob/drone-service/app/controllers/projects/merge_requests_controller.rb#L180
- https://gitlab.com/bugagazavr/gitlab-ce/blob/drone-service/app/helpers/merge_requests_helper.rb#L37
- https://gitlab.com/bugagazavr/gitlab-ce/blob/drone-service/app/models/project_services/ci_service.rb#L55
- https://gitlab.com/bugagazavr/gitlab-ce/blob/drone-service/app/models/project_services/buildkite_service.rb#L53
- https://gitlab.com/bugagazavr/gitlab-ce/blob/drone-service/app/models/project_services/bamboo_service.rb#L109
- https://gitlab.com/bugagazavr/gitlab-ce/blob/drone-service/lib/gitlab/backend/grack_auth.rb#L67
Why was this MR needed?:
One more integrated service (: