Convert keystone to use uwsgi with the proxy

This makes keystone use the proxy uwsgi module when running in uwsgi
mode. It also introduces a new stackrc variable which is WSGI_MODE
that we can use to control the conditionals in services that current
work with mod_wsgi.

Also update retry timeouts on proxy pass so that workers don't disable
their connections during polling for initial activity.

Change-Id: I46294fb24e3c23fa19fcfd7d6c9ee8a932354702

lib/apache

@@ -260,7 +260,7 @@ function write_uwsgi_config {
     else
         local apache_conf=""
         apache_conf=$(apache_site_config_for $name)
-        echo "ProxyPass \"${url}\" \"unix:${socket}|uwsgi://uwsgi-uds-${name}/\"" | sudo tee $apache_conf
+        echo "ProxyPass \"${url}\" \"unix:${socket}|uwsgi://uwsgi-uds-${name}/\" retry=0 " | sudo tee $apache_conf
         enable_apache_site $name
         reload_apache_server
     fi