Fa tracking/seeding mask has wrong datatype

[frheault]

mrcalc $fa $params.pft_fa_seeding_mask_theshold -ge ${sid}__pft_seeding_mask.nii.gz
(Same for local) requires -datatype as uint8
Or use scil_image_math.py convert --data_type

This makes the pipeline crash at tracking.
OSError: The image me_s0__local_tracking_mask.nii.gz cannot be loaded as mask because its type <class 'numpy.float32'> is not compatible with a mask