TEST: added test for sct_otsu
TEST: added test for sct_otsu

Former-commit-id: 6a6345f40317084ebd2dcd8a065bb3825f5f1cd9 [formerly a24c637b289cc62da01e499e75810549c9848256]
Former-commit-id: 7fde57b52ee3682547b66a9ad73d14d8d121eaca
Former-commit-id: 0243b1e80eab780579a12f87d18e5bc76ed142d7
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox