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>
Merge pull request #2354 from dachary/wip-9273-mon-preload-erasure-code

erasure-code: preload the default plugins in the mon

Reviewed-by: Sage Weil <sage@redhat.com>