neutron: Wait until ovs-vswitchd creates the bridge

Seeing a race condition where lib/neutron code tries to
set the MTU on br-ex before it exists.

Thanks to some good grepping by sdague, it appears that the difference
between lib/neutron and lib/neutron-legacy is that the initial bridge
being created is br-int while in lib/neutron the initial bridge
created is br-ex, which means there must be some kind of warm-up that
occurs between the first bridge that is created by ovs-vswitchd and the
second, and the second one created is much faster.

So instead, let's just wait for the bridge to be created successfully.

Change-Id: I271dc8b6ae5487c80d2a22153b3fc45fb247707f
diff --git a/lib/neutron_plugins/ovs_base b/lib/neutron_plugins/ovs_base
index 9e1421f..f6d10ea 100644
--- a/lib/neutron_plugins/ovs_base
+++ b/lib/neutron_plugins/ovs_base
@@ -19,7 +19,7 @@
 
 function _neutron_ovs_base_add_bridge {
     local bridge=$1
-    local addbr_cmd="sudo ovs-vsctl --no-wait -- --may-exist add-br $bridge"
+    local addbr_cmd="sudo ovs-vsctl -- --may-exist add-br $bridge"
 
     if [ "$OVS_DATAPATH_TYPE" != "system" ] ; then
         addbr_cmd="$addbr_cmd -- set Bridge $bridge datapath_type=${OVS_DATAPATH_TYPE}"