Extra logging for LTI class list sync.

This is a lighter debug log for use on prod where enabling debug is a
bit unmanagable.

Some users are being dropped from a course and then re-added later. This
log will give more information on the xml class list transmitted by
Connect during sync. Information provided includes the raw XML or the
failure reason if sync failed. Three failures are checked: cannot
connect to Connect, invalid XML causing parsing failure, and if XML
returned indicated a failure.

The log file is hard coded to live in logs/lti_xml.log