Utility silently fails to add EXIF data if exiftool is not in path

[eli-hu]

https://github.com/uhlibraries-digital/tdd/blob/master/lib/tdd.rb#L149 makes a system call to exiftool but does not capture any errors, so if exiftool is not in the path, this call fails to add EXIF data to the PDF but also does not log any errors or alert the user that there's anything wrong.

Also, https://github.com/uhlibraries-digital/tdd/blob/master/tdd-workflow-utility.rb#L337 gets the location of the exiftool from the paths.yml config, but never uses it. We don't seem to be using MiniExifTool at all.