erasure-code: mkfs.sh needs to know the plugin directory

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
erasure-code: use s/get_str_map/get_json_str_map/

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
Merge pull request #2359 from dachary/wip-fix-lrc

fix lrc tests and prototype 

Reviewed-by: Sage Weil <sage@redhat.com>