Historically, we've allowed objects to get on disk that may not have had
all of their required EC metadata. Add a new method to sanity-check
metadata in the auditor, and quarantine such invalid data.
Additionally, call validation early in the reconstructor's
reconstruct_fa() method so we do not have to attempt reconstruction for
invalid EC fragments.
Change-Id: I73551007843d27041f594923c59e6fd89caf17e5
745a7f04fe