ceph_test_rados_api_tier: improve promote+scrub test

We need to have multiple clones with some different patterns of
missing-ness.

Signed-off-by: Sage Weil <sage@inktank.com>
osd/ReplicatedPG: fix cache tier scrub again

This condition was flipped from commit eb71924ea27e78d97bd45674ef5e6a7f
and the test case in c3292e48483d861148322590ea1f05afd28cc2d3 still didn't
catch it.  (It does now.)

Signed-off-by: Sage Weil <sage@inktank.com>