mon: OSDMonitor: limit tier-specific pool set/get on non-tier pools

Fixes: 8696

Also has a few other patches addressing some miscelaneous stuff such as:

- make sure to clear tier-specific fields from pg_pool_t when removing a tier
- be really verbose on inconsistency when removing a tier
- some workunits for all of the above
- some fixes on qa/workunits/cephtool/test.sh for those tests that were setting
and getting some tier-specific variables on non-tier pools.