osd: build_simple creates a single rule

osd: build_simple creates a single rule

The three rules created by build_simple are identical. They are replaced
by a single rule named replicated_rule which is set to be used by the
data, rbd and metadata pools.

Instead of hardcoding the ruleset number to zero, it is read from
osd_pool_default_crush_ruleset which defaults to zero.

The CEPH_DEFAULT_CRUSH_REPLICATED_RULESET enum is moved from osd_type.h to
config.h because it may be needed when osd_type.h is not included.

Signed-off-by: Loic Dachary <loic@dachary.org>