erasure-code: preload the default plugins in the mon

The commit 164f1a1959a863848319585fa752250c7b261381 preloads the
jerasure plugin 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 #2356 from dachary/wip-9273-mon-preload-erasure-code-firefly

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