erasure-code: isa plugin thrashods suite

Add the distros directory which enumerates the os_type and
os_version on which the suite is to run.

http://tracker.ceph.com/issues/9660 Fixes: #9660

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
(cherry picked from commit 16e564ec8dea1649888847102ea39fa082e4d3f2)
Merge pull request #205 from dachary/wip-erasure-code-isa-giant

erasure-code: isa plugin thrashods suite

Reviewed-by: Samuel Just <sam.just@inktank.com>