erasure-code: preload LRC plugin

Add LRC to the list of erasure code plugins preloaded by default.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
erasure-code: lowercase LRC plugin name

So that all erasure code plugins are lowercase.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
Merge pull request #2358 from dachary/wip-lrc

rename LRC to lrc + preload

Reviewed-by: Sage Weil <sage@redhat.com>