Use (or set properly) system-id generated by openvswitch

In case when OVN_UUID isn't set by user, and it isn't stored
in /etc/openvswith/system-id.conf file, Devstack will reuse it.
If it's not, it will generate and store it in the
/etc/openvswitch/system-id.conf file so it can be set to same value
after openvswitch will be e.g. restarted.

In case when OVN_UUID is set by user, it will be also saved in
/etc/openvswitch/system-id.conf file to make it persistent when e.g
openvswitch will be restarted.

Closes-Bug: #1918656
Change-Id: I8e3b05f3ab83e204bc1ce895baec0e1ba515895b

Author: slawqo

lib/neutron_plugins/ovn_agent

@@ -66,7 +66,9 @@ OVN_L3_SCHEDULER=${OVN_L3_SCHEDULER:-leastloaded}
 
 # A UUID to uniquely identify this system.  If one is not specified, a random
 # one will be generated.  A randomly generated UUID will be saved in a file
-# 'ovn-uuid' so that the same one will be re-used if you re-run DevStack.
+# $OVS_SYSCONFDIR/system-id.conf (typically /etc/openvswitch/system-id.conf)
+# so that the same one will be re-used if you re-run DevStack or restart
+# Open vSwitch service.
 OVN_UUID=${OVN_UUID:-}
 
 # Whether or not to build the openvswitch kernel module from ovs.  This is required
@@ -109,6 +111,7 @@ OVS_RUNDIR=$OVS_PREFIX/var/run/openvswitch
 OVS_SHAREDIR=$OVS_PREFIX/share/openvswitch
 OVS_SCRIPTDIR=$OVS_SHAREDIR/scripts
 OVS_DATADIR=$DATA_DIR/ovs
+OVS_SYSCONFDIR=${OVS_SYSCONFDIR:-/etc/openvswitch}
 
 OVN_DATADIR=$DATA_DIR/ovn
 OVN_SHAREDIR=$OVS_PREFIX/share/ovn
@@ -521,11 +524,17 @@ function configure_ovn {
     echo "Configuring OVN"
 
     if [ -z "$OVN_UUID" ] ; then
-        if [ -f ./ovn-uuid ] ; then
-            OVN_UUID=$(cat ovn-uuid)
+        if [ -f $OVS_SYSCONFDIR/system-id.conf ]; then
+            OVN_UUID=$(cat $OVS_SYSCONFDIR/system-id.conf)
         else
             OVN_UUID=$(uuidgen)
-            echo $OVN_UUID > ovn-uuid
+            echo $OVN_UUID | sudo tee $OVS_SYSCONFDIR/system-id.conf
+        fi
+    else
+        local ovs_uuid
+        ovs_uuid=$(cat $OVS_SYSCONFDIR/system-id.conf)
+        if [ "$ovs_uuid" != $OVN_UUID ]; then
+            echo $OVN_UUID | sudo tee $OVS_SYSCONFDIR/system-id.conf
         fi
     fi