erasure-code: enclose no-lrc in a task

http://tracker.ceph.com/issues/9841 Fixes: #9841

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
Merge pull request #201 from dachary/wip-9841-no-lrc

erasure-code: enclose no-lrc in a task