osd/OSDMap: set pg_autoscale_mode with setting from conf

osd/OSDMap: set pg_autoscale_mode with setting from conf

* update build_simple_optioned() to set pg_autoscale_mode with the setting
  read from conf, otherwise it will be a random value in heap.
* update cli test accordingly, otherwise we will have

/home/jenkins-build/build/workspace/ceph-pull-requests/src/test/cli/osdmaptool/create-racks.t:
failed
---
/home/jenkins-build/build/workspace/ceph-pull-requests/src/test/cli/osdmaptool/create-racks.t
+++
/home/jenkins-build/build/workspace/ceph-pull-requests/src/test/cli/osdmaptool/create-racks.t.err
@@ -796,7 +796,7 @@
   nearfull_ratio 0
   min_compat_client jewel

-  pool 1 'rbd' replicated size 3 min_size 2 crush_rule 0 object_hash
rjenkins pg_num 15296 pgp_num 15296 last_change 0 flags hashpspool
stripe_width 0 application rbd
+  pool 1 'rbd' replicated size 3 min_size 2 crush_rule 0 object_hash
rjenkins pg_num 15296 pgp_num 15296 autoscale_mode ??? last_change 0
flags hashpspool stripe_width 0 application rbd

Signed-off-by: Kefu Chai <kchai@redhat.com>