Buffer logger rails 4

The regression we saw on logs today was because btwn rails3 and 4, the class `Logger` has different behaviour.

see 
https://github.com/rails/rails/blob/3-2-stable/activesupport/lib/active_support/core_ext/logger.rb
https://github.com/rails/rails/blob/4-0-stable/activesupport/lib/active_support/core_ext/logger.rb

### Problem
We can see that `Logger` monkey-patch on rails4 was deprecated, so they dont `require` that anymore. The thing is that the monkey-patch they had was pushing a `SimpleFormatter` as the formatter of all `Logger` classes. So thats why the prefix was not showing up. When we upgrade to rails4, that monkey patch doesn't happen anymore, so `Logger` will use the default formatter, see, http://www.ruby-doc.org/stdlib-2.1.0/libdoc/logger/rdoc/Logger.html#class-Logger-label-Format.


### Solution
Use AS::Logger instead, which is the one that has a formatter that doesn't add any prefix.

review @camilo @samuelkadolph @dylanahsmith