ceph-facts: move facts to defaults value

ceph-facts: move facts to defaults value

There's no need to define a variable via a fact if we can do it via a
default value. Using a fact could be interesseting to override the
default value on some condition.

- ceph_uid could be set to 167 by default because it's only different on
non containerized deployment on Debian/Ubuntu.
- rbd_client_directory_{owner,group,mode} could be set to ceph,ceph,0770
by default install of null as we are doing in the facts.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>