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>
Actually this part of logic is kind of complicated.

According to https://github.com/ceph/ceph/blob/master/src/mon/OSDMonitor.cc#L5116, 
When crush-ruleset-name is emply, Only if it's a erasure pool with profile named "default", the ruleset-name will be set to "erasure-code", otherwise it will implicitly use ruleset named after the pool.

And, if the specified ruleset doesn't exist, for replicated pool ,it will fall back to default( osd_pool_default_crush_replicated_ruleset , as shown in this patch), but for EC pool, it will create a new ruleset with the specified name(see https://github.com/ceph/ceph/blob/master/src/mon/OSDMonitor.cc#L3088)

I think this logic do make sense but  too complicated for user, especially EC and replicated pool  have different logic and default value.