Make sure ComputeDVARS get the appropriate mask

[oesteban]

After merging #743 we have:
https://320-53608443-gh.circle-artifacts.com/0/home/ubuntu/ds054/out/fmriprep/sub-100185.html

[oesteban]

Oh wait, is that the fake error we introduced to check that errors are actually included in the report?

[effigies]

Yup. Check the timestamp in the filename:

/out/fmriprep/sub-100185/log/20171011-011937_b1e41dbc-a9df-45a8-b541-e0b7897ca010/crash-20170905-182839-root-dvars-b78e9ea8-e295-48a1-af71-2d36afd9cebf.txt