Flag Former Students in the sync process

Once a student has graduated they tend to have strange entries in the
directory.  This adds a place for an LDAP query which will only return
former students and they can then be flagged that way so some mis-match
statuses will be ignored.
Students are never unfledged from this automatically, this has to be
done in the management console UI where they can also be flagged
manually.
Fix comments in StudentProcess

Re-ordered the steps to match what is now happening.
Fix build property for former student filter.
Add migration for former student role
Make sure former students don't become students

Fix a refactoring mistake that was setting all former students to
students when they were updated.
Merge pull request #697 from jrjohnson/edssync

Flag Former Students in the sync process