deprecate `wsgi_log_format` config variable

Running under a real wsgi environment, such as uwsgi or apache /
mod_wsgi is preferred now, and there is a different logging solution
for that. This was always an eventlet leaky abstraction. So we'll just
deprecate this for now, and the code can be removed once eventlet on
the API side is removed.

Change-Id: I934a1693cbfd539d8575d022519510d19d13aaab

nova/conf/wsgi.py

@@ -45,12 +45,22 @@ Possible values:
         default='%(client_ip)s "%(request_line)s" status: %(status_code)s'
                 ' len: %(body_length)s time: %(wall_seconds).7f',
         deprecated_group='DEFAULT',
+        deprecated_for_removal=True,
+        deprecated_since='16.0.0',
+        deprecated_reason="""
+This option only works when running nova-api under eventlet, and
+encodes very eventlet specific pieces of information. Starting in Pike
+the preferred model for running nova-api is under uwsgi or apache
+mod_wsgi.
+""",
         help="""
 It represents a python format string that is used as the template to generate
 log lines. The following values can be formatted into it: client_ip,
 date_time, request_line, status_code, body_length, wall_seconds.
 
-This option is used for building custom request loglines.
+This option is used for building custom request loglines when running
+nova-api under eventlet. If used under uwsgi or apache, this option
+has no effect.
 
 Possible values:
 

releasenotes/notes/deprecate_wsgi_log_format-43a10b7a608ea8f3.yaml

@@ -0,0 +1,6 @@
+---
+deprecations:
+  - |
+    Configuration option ``wsgi_log_format`` is deprecated. This only
+    applies when running nova-api under eventlet, which is no longer
+    the preferred deployment mode.