ceph_test_rados_api_tier: fix [EC] HitSet{Read,Write,Trim} tests

The hit_set_ fields can only be set on tier pools as of
f131dfbaedf6f451572e7aa3a83f653912122953.

Fixes: #8823
Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #2102 from ceph/wip-8823

ceph_test_rados_api_tier: fix [EC] HitSet{Read,Write,Trim} tests

Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>