Make the logging_rpc member a class property

The ``LoggingServiceDriverManager`` can register additional drivers by
calling the method ``register_driver``. Depending on the driver type,
the logging plugin will require RPC.

Before this patch, the RPC server was loaded at the beginning, using
the initial ``rpc_required`` value. If the initial driver doesn't
require RPC, the RPC server was never loaded, regardless of future
registered drivers.

Within in this patch, the RPC server instance is a property that
depends on the current ``rpc_required`` and the private variable storing
the RPC instance. If the ``rpc_required`` flag changes, the next time
the RPC server is required it will be loaded.

Closes-Bug: #2141308
Signed-off-by: Rodolfo Alonso Hernandez <ralonsoh@redhat.com>
Change-Id: I4e7c773d19d189535fa6118e1f2d0c2a088010e4
(cherry picked from commit 1f953df)

Author: ralonsoh

neutron/services/logapi/drivers/manager.py

@@ -68,14 +68,18 @@ def __init__(self):
         self._drivers = set()
         self.rpc_required = False
         registry.publish(log_const.LOGGING_PLUGIN, events.AFTER_INIT, self)
-
-        if self.rpc_required:
-            self.logging_rpc = server_rpc.LoggingApiNotification()
+        self._logging_rpc = None
 
     @property
     def drivers(self):
         return self._drivers
 
+    @property
+    def logging_rpc(self):
+        if self.rpc_required and not self._logging_rpc:
+            self._logging_rpc = server_rpc.LoggingApiNotification()
+        return self._logging_rpc
+
     def register_driver(self, driver):
         """Register driver with logging plugin.