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>
(cherry picked from commit e17e9d857722ee478abda10adb32e15b11fff2ff)