erasure-code: workunit to check for encoding regression

Clone the archive of encoded objects and decode all archived objects, up
to and including the current ceph version.

http://tracker.ceph.com/issues/9420 Refs: #9420

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
erasure-code: add corpus verification to make check

Signed-off-by: Loic Dachary <loic-201408@dachary.org>