Enable oslo_config mutable configurations

This patch enables oslo_config mutable configuration for the Qinling
control plane processes. The configuration will be updated when the
parent process receives a HUP signal.
This completes the Rocky goal: Enable mutable configuration.

Change-Id: Ib4b007d0c1e0401ed652bdf7a90993200bbfb576
Story: 2001545
Task: 6400

qinling/cmd/api.py

@@ -38,7 +38,8 @@ def main():
         rpc.get_transport()
 
         api_server = api_service.WSGIService()
-        launcher = service.launch(CONF, api_server, workers=api_server.workers)
+        launcher = service.launch(CONF, api_server, workers=api_server.workers,
+                                  restart_method='mutate')
         launcher.wait()
     except RuntimeError as excp:
         sys.stderr.write("ERROR: %s\n" % excp)

qinling/cmd/engine.py

@@ -15,6 +15,7 @@
 import sys
 
 import cotyledon
+from cotyledon import oslo_config_glue
 from oslo_config import cfg
 from oslo_log import log as logging
 
@@ -39,6 +40,7 @@ def main():
             eng_service.EngineService,
             workers=1,
         )
+        oslo_config_glue.setup(sm, CONF, reload_method="mutate")
         sm.run()
     except RuntimeError as excp:
         sys.stderr.write("ERROR: %s\n" % excp)

releasenotes/notes/enable-mutable-configuration-a0527660fa58532c.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Operators can now update the running configuration of the Qinling control
+    plane processes by sending the parent process a "HUP" signal.
+    Note: The configuration option must support mutation.