Octavia devstack plugin API mode

For API drivers which only use API service, devstack needs:
- To skip creation of o-oh0 interface, as there's no amphora VMs
- Create endpoint, roles

Change-Id: I168b9ccc968a680ed2db326435f7523c35e7a020

devstack/plugin.sh

@@ -442,7 +442,7 @@ function configure_octavia_api_haproxy {
 
 function octavia_start {
 
-    if  ! ps aux | grep -q [o]-hm0 ; then
+    if  ! ps aux | grep -q [o]-hm0 && [ $OCTAVIA_NODE != 'api' ] ; then
         sudo dhclient -v o-hm0 -cf $OCTAVIA_DHCLIENT_CONF
     fi
 
@@ -572,6 +572,15 @@ function octavia_init {
            configure_octavia_tempest ${OCTAVIA_AMP_NETWORK_ID}
        fi
 
+       add_load-balancer_roles
+   elif [ $OCTAVIA_NODE == 'api' ] ; then
+       create_octavia_accounts
+
+       # Adds service and endpoint
+       if is_service_enabled tempest; then
+           configure_octavia_tempest ${OCTAVIA_AMP_NETWORK_ID}
+       fi
+
        add_load-balancer_roles
    fi