TEST: correct output path for register graymatter
TEST: correct output path for register graymatter

Former-commit-id: 4695c83045fbece66a95970177df842c87dbdd28 [formerly 77106e94a531396b48da50bab113cd58ac9d0905]
Former-commit-id: e1a07eaa51c50ad2f7d753436f51176a9323ffbf
Former-commit-id: 369db3582cddcccd4fa5376eb94b2e75e06ac044
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox