retire async

Let me retire background posting once because I met troubles that fluentd process does not die. 
https://gist.github.com/sonots/8780628

httpclient is stuck at /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/httpclient-2.3.4.1/lib/httpclient/session.rb:879:in `block in parse_header', and timeout parameter does not work well in asyncronous version.