[autohelp] Use oslo_config.generator if possible

Options discovery is 1) complex and 2) partly broken at the moment. This
patch adds the ability to use the oslo.config generator to discover
options.

This is a quick fix to restore some missing options but is porbably not
a definitive solution.

Ways to improve things:
- get rid of all the discovery code and only use the oslo generator
- make use of the YAML output from oslo.config (WIP):
  . https://review.openstack.org/#/c/451081/
  . https://review.openstack.org/#/c/458556/

Change-Id: Iaabb5418b103f20bb13c6843482277579e77b51b
Partial-Bug: #1668202

autogenerate_config_docs/autohelp.py

@@ -30,6 +30,7 @@ import sys
 import jinja2
 import stevedore
 
+from oslo_config import generator
 try:
     from sqlalchemy import exc
 except Exception:
@@ -677,6 +678,25 @@ def main():
     options = OptionsCache(overrides, verbose=args.verbose)
     options.maybe_load_extensions(args.repos)
 
+    # NOTE(gpocentek): most projects have moved to oslo_config.generator to
+    # handle their opt files. We try to use it and add the new options.
+    # We should probably only use this at some point (here or in a sphinx
+    # extension).
+    try:
+        generator_opts = generator._list_opts(package_name)[0][1]
+    except Exception as e:
+        generator_opts = None
+
+    if generator_opts is not None:
+        for grouped_opts in generator_opts:
+            group = grouped_opts[0]
+            for opt in grouped_opts[1]:
+                if group in ('DEFAULT', None):
+                    optname = opt.name
+                else:
+                    optname = '%s/%s' % (group, opt.name)
+                options._add_opt(optname, group, opt)
+
     if args.verbose > 0:
         print("%s options imported from package %s." % (len(options),
                                                         str(package_name)))