unit_testing/test_metadata.py: use get_indiv_label_ids
unit_testing/test_metadata.py: use get_indiv_label_ids


Former-commit-id: 5f7164ef58e8b99045519cce123a4f4322028839
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox