CrushWrapper: pick a ruleset same as rule_id

Originally in the add_simple_ruleset funtion, the ruleset_id
is not reused but rule_id is reused. So after some add/remove
against rules, the newly created rule likely to have
ruleset!=rule_id.

We dont want this happen because we are trying to hold the constraint
that ruleset == rule_id.

This patch allow ruleset_id be reused. After having this patch,
add/remove rules will not break the constraint.

Signed-off-by: Xiaoxi Chen <xiaoxi.chen@intel.com>
To have a crushmap with **ruleset != ruleid** you can generate such a map with ceph without your patch and save it in the test directory. Because after your patch is applied there will be no way to create such a situation without writing a program to do so. You can see examples of using a crushmap in https://github.com/ceph/ceph/tree/master/src/test/cli/crushtool and https://github.com/ceph/ceph/blob/master/src/test/cli/crushtool/five-devices.crushmap