comment update, now that module imports are gone

Reviewers: sean

Reviewed By: sean

Differential Revision: https://phabricator.buildinspace.com/D107
when printing errors, only add a newline if there isn't one already

Summary:
Some errors include subprocess output, which is already
newline-terminated.

Reviewers: sean

Reviewed By: sean

Differential Revision: https://phabricator.buildinspace.com/D106
start using subprocess.DEVNULL again

Summary:
We stopped using this for 3.2 compatibility, but now that we're >=3.3 we
can bring it back.

Reviewers: sean

Reviewed By: sean

Differential Revision: https://phabricator.buildinspace.com/D103