Accept error code 204 (no content) if no jobs in queue
Accept error code 204 (no content) if no jobs in queue

Closes !36

hu19891110/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner