I'm not a fan of having these constants here.  I'm actually wondering if we should:

- rename these CEPH_DEFAULT_REPLICATED_RULE, cEPH_DEFAULT_ERASURE_RULE, for use by OSDMap::create_*.
- make the defaults explicit (and match) in config_opts.h
- make the old osd_pool_default_rule override them; this way the default is visible in config_opts.h (and ceph-$whatever --show-config)
- make the initial crush map only have 2 rules (default_replicated and default_erasure, perhaps).  users can create new rule(s) if/when they want them to diverge.

?