servlet: fix a couple of issues

* Fix typos in http_servlet.rb
* Add missing require in plugin.rb

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
servlet: tidy up integration

* Make the LogService bridge available to the plugin
* Fix path to the config.ru file
* Make the rake task bundle the config.ru file, if available

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
Merge branch 'master' of github.com:killbill/killbill-plugin-framework-ruby