erasure-code: CEPH_FEATURE_ERASURE_CODE_PLUGINS_V2 integration tests

http://tracker.ceph.com/issues/9343 Refs: #9343

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

s
erasure-code: assert that firefly-x/stress-split cannot load lrc

Because it would crash existing plugins.

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