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>
<pre>
if ! $TEST_function $dir ; then
 cat $dir/a/log
 return 1
fi
</pre>

should be preserved so that the output contains the logs when it fails. Since the test directory is removed at the end of the test when it completes, the logs would otherwise be lost.