[queens] Smooth out OVN backend

* add missing ovn control options file
* install networking_ovn package before db_sync
* set sync mode of ovn northbound OVSDB with neutron DB
* enable distributed floating IP support if DVR is turned on

Change-Id: I1ece368e8d763fa7c96b1853646e90d5c1fb11e0
diff --git a/README.rst b/README.rst
index 9cbd45a..dd03ed1 100644
--- a/README.rst
+++ b/README.rst
@@ -829,6 +829,9 @@
             ovn:
               driver: ovn
           tenant_network_types: "geneve,flat"
+          ovn:
+            ovn_l3_scheduler: leastloaded # valid options: chance, leastloaded
+            neutron_sync_mode: repair # valid options: log, off, repair
         ovn_ctl_opts:
           db-nb-create-insecure-remote: 'yes'
           db-sb-create-insecure-remote: 'yes'