mon/OSDMonitor : Use user provided ruleset for replicated pool

When creating a replicated pool, currently ceph ignore the ruleset
name provided by user but use a global default ruleset.

This patch fix this bug, so the rulset specified by
 ceph osd pool create <pg_num> <pgp_num> replicated <my_ruleset_name>
can be properly set.

Signed-off-by: Xiaoxi Chen <xiaoxi.chen@intel.com>
The case where the ruleset_name is in the pending crushmap should be handled with something similar to
<pre>
  CrushWrapper newcrush;
  _get_pending_crush(newcrush);

  *ruleset = newcrush.get_rule_id(ruleset_name);
</pre>