Fix Horizon WSGI application log parsing

Like other WSGI services in Kolla Ansible, the Horizon WSGI application
handles log output via the `wsgi.errors` object. See [1] for further
information. The problem is that this log output is written to a file called
`horizon.log`, causing it to processed as an 'Oslo log' in the Fluentd
processing pipeline. Since the log format doesn't match the expected format,
this results in parsing errors.

This fix renames the log file and adjusts the format to match other WSGI
applications. The logs are then processed in the same way as other WSGI
application logs, resolving the issue.

[1] https://modwsgi.readthedocs.io/en/master/user-guides/debugging-techniques.html

Change-Id: I93777d1c53920f5470c78356e6b3a4064fbe04b4
Closes-Bug: #1898174

ansible/roles/horizon/templates/horizon.conf.j2

@@ -15,7 +15,8 @@ TraceEnable off
 
 <VirtualHost {{ api_interface_address }}:{{ horizon_listen_port }}>
     LogLevel warn
-    ErrorLog /var/log/kolla/horizon/horizon.log
+    ErrorLogFormat "%{cu}t %M"
+    ErrorLog /var/log/kolla/horizon/horizon-error.log
     LogFormat "%{X-Forwarded-For}i %l %u %t \"%r\" %>s %b %D \"%{Referer}i\" \"%{User-Agent}i\"" logformat
     CustomLog /var/log/kolla/horizon/horizon-access.log logformat
 

releasenotes/notes/horizon-log-bugfix-b89f502c2f3ccaf9.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fixes an issue where Fluentd was parsing Horizon WSGI application logs
+    incorrectly.
+    Horizon error logs are now written to ``horizon-error.log`` instead of
+    ``horizon.log``.
+    See `LP#1898174 <https://bugs.launchpad.net/kolla-ansible/+bug/1898174>`__