osd: use CrushWrapper::add_simple_ruleset

osd: use CrushWrapper::add_simple_ruleset

Replace the manually crafted ruleset in OSDMap::build_simple_crush_map*
with calls to add_simple_ruleset. The generated ruleset do not have the
same behavior but that presumably do not cause any backward
compatibility problem because they are only created when a new cluster
is being initialized.

The prototypes of OSDMap::build_simple* are modified to allow for a
return code and display of a human readable error message.

The --osd-min-rep and --osd-max-rep configuration options are removed :
they were only used in the code that was removed.

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