erasure-code: upgrade/firefly-x/stress-split-erasure-code

Mimic upgrade/firefly-x/stress-split only with thrashosd configured with
min_in: 4 for k=3,m=1 . All erasure code workloads are moved in this
dedicated suite.

http://tracker.ceph.com/issues/9652 Fixes: #9652

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