Log command errors using Errorf
Log command errors using Errorf

Summary: fixes #53

Reviewers: emso

Reviewed By: emso

Differential Revision: https://phabricator-dot-shipshapecode.appspot.com/D44

google/shipshape,google/shipshape,google/shipshape,google/shipshape,google/shipshape,google/shipshape,google/shipshape