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>
(cherry picked from commit 98ef86a202a26682f74c6d7b7aef4616fcc4b128)
Merge pull request #202 from dachary/wip-9841-no-lrc-giant

erasure-code: enclose no-lrc in a task (giant)