erasure-code: preload the default plugins in the mon

The commit 9b802701f78288ba4f706c65b853415c69002d27 preloads the
supported plugins in the OSD. They must also be preloaded in the mon for
the same reasons.

http://tracker.ceph.com/issues/9273 Fixes: #9273

Signed-off-by: Loic Dachary <loic-201408@dachary.org>