Enable healthcheck middleware

The healthcheck middleware from oslo.middleware library is now commonly
enabled in OpenStack services, for service healthcheck (often used by
load balancers such as haproxy). This enables the middleware so that
operators can use the healthcheck endpoint more easily. This also
replaces the oslo.middleware config entry point by more specific sub
entry points, to avoid rendering options from unused middlewares such
as sizelimit.

Change-Id: If3296e651e7f20a3f5314c085cc99ce4b004c065

etc/trove/api-paste.ini

@@ -1,6 +1,7 @@
 [composite:trove]
 use = call:trove.common.wsgi:versioned_urlmap
 /: versions
+/healthcheck: healthcheck
 /v1.0: troveapi
 
 [app:versions]
@@ -42,5 +43,10 @@ paste.app_factory = trove.common.api:app_factory
 [filter:debug]
 paste.filter_factory = trove.common.wsgi:Debug
 
+[app:healthcheck]
+paste.app_factory = oslo_middleware:Healthcheck.app_factory
+backends = disable_by_file
+disable_by_file_path = /etc/trove/healthcheck_disable
+
 [filter:http_proxy_to_wsgi]
 use = egg:oslo.middleware#http_proxy_to_wsgi

releasenotes/notes/healthcheck-middleware-670a667bfb245123.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Now the healthcheck middleware from oslo.middleware library is enabled by
+    default. Edit ``api-paste.ini`` to disable the middlewware.

tools/trove-config-generator.conf

@@ -3,7 +3,9 @@ output_file = etc/trove/trove.conf.sample
 wrap_width = 79
 namespace = trove.config
 namespace = oslo.messaging
-namespace = oslo.middleware
+namespace = oslo.middleware.cors
+namespace = oslo.middleware.healthcheck
+namespace = oslo.middleware.http_proxy_to_wsgi
 namespace = oslo.log
 namespace = oslo.policy
 namespace = osprofiler