Add oslo_config program support to paste middleware

oslo_config's configfile autodiscovery permits an additional parameter
named 'prog', which will add an additional file name to the possible
files that are checked in oslo_config directories. This patch adds this
parameter to paste-ini initialization, permitting access to more
configuration files.

This feature is required by glance, as glance does not make use of
./glance/glance.conf. Instead, they use ./glance/glance-api.conf. The
appropriate middleware configuration in this case would then be:

oslo_config_project=glance
oslog_config_program=glance-api

Change-Id: Ie530e4fac8076dc46b705770d12940ef91cb4644

doc/source/cors.rst

@@ -104,6 +104,16 @@ will add CORS support. To add multiple domains, simply add another filter.::
     allow_headers=Content-Type,Cache-Control,Content-Language,Expires,Last-Modified,Pragma,X-Custom-Header
     expose_headers=Content-Type,Cache-Control,Content-Language,Expires,Last-Modified,Pragma,X-Custom-Header
 
+If your application is using pastedeploy, but would also like to use the
+existing configuration from oslo_config in order to simplify the points of
+configuration, this may be done as follows.::
+
+    [filter:cors]
+    paste.filter_factory = oslo_middleware.cors:filter_factory
+    oslo_config_project = oslo_project_name
+
+    # Optional field, in case the program name is different from the project:
+    oslo_config_program = oslo_project_name-api
 
 Configuration Options
 ---------------------

doc/source/oslo_config.rst

@@ -29,6 +29,10 @@ The paste filter (in /etc/my_app/api-paste.ini) will looks like::
     # the application configuration, by setting this:
     #  oslo_config_project = my_app
 
+    # In some cases, you may need to specify the program name for the project
+    # as well.
+    #  oslo_config_program = my_app-api
+
 The oslo.config file of the application (eg: /etc/my_app/my_app.conf) will looks like::
 
     [oslo_middleware]

oslo_middleware/base.py

@@ -67,8 +67,16 @@ class ConfigurableMiddleware(object):
                     default_config_files = [self.conf['oslo_config_file']]
                 else:
                     default_config_files = None
+
+                if 'oslo_config_program' in self.conf:
+                    program = self.conf['oslo_config_program']
+                else:
+                    program = None
+
                 self.oslo_conf = cfg.ConfigOpts()
-                self.oslo_conf([], project=self.conf['oslo_config_project'],
+                self.oslo_conf([],
+                               project=self.conf['oslo_config_project'],
+                               prog=program,
                                default_config_files=default_config_files,
                                validate_default_values=True)