neorados: build new RADOS client using legacy librados::Rados

neorados: build new RADOS client using legacy librados::Rados

Client libraries like librbd cannot force the adaptation to neorados
and it would not be ideal to have two effective RADOS cluster
connections for librados and neorados.

The new neorados::RADOS::make_with_librados helper method will
allow neorados to re-use the existing thread pool, MGR, MON, and
objecter already created for librados::Rados.

Signed-off-by: Jason Dillaman <dillaman@redhat.com>