Only output Server logs in Development

Right now when you start a server via `rails s`, the logger gets extended so that it logs to the file system and also to stdout. This extension behavior is not "intelligent" and if the default logger is already set to output to stdout, then the contents will be received twice.

To capture logs in accordance with http://www.12factor.net/logs some platforms require the logs to be sent to standard out. If a logger is set to stdout, and the server is started using `rails server` instead of another method (i.e. `thin start` etc.) then the app will produce double logs.

This PR fixes the issue by only extending the logger to standard out in the development environment. So that in production you don't get double logs like this:

```
ActionView::Template::Error (wrong number of arguments (5 for 4)):
    1: <% lang_index = 0 %>
    2: <div class="row">
    3:   <ul class="nav nav-tabs nav-stacked span2" data-tabs="tabs" id="repo-tabs">
    4:     <% repos.group_by(&:language).each do |lang, repos| %>
    5:       <% unless lang == nil %>
    6:         <li><a href="#<%= "#{lang.parameterize}#{lang.hash}" %>" data-toggle="tab"><%= lang %></a></li>
    7:       <% end -%>
  app/views/shared/_repos.html.erb:4:in `_app_views_shared__repos_html_erb___1685450633638247395_70300668607000'
  app/views/pages/index.html.erb:13:in `_app_views_pages_index_html_erb__2084723628308867770_70300687584880'

ActionView::Template::Error (wrong number of arguments (5 for 4)):
    1: <% lang_index = 0 %>
    2: <div class="row">
    3:   <ul class="nav nav-tabs nav-stacked span2" data-tabs="tabs" id="repo-tabs">
    4:     <% repos.group_by(&:language).each do |lang, repos| %>
    5:       <% unless lang == nil %>
    6:         <li><a href="#<%= "#{lang.parameterize}#{lang.hash}" %>" data-toggle="tab"><%= lang %></a></li>
    7:       <% end -%>
  app/views/shared/_repos.html.erb:4:in `_app_views_shared__repos_html_erb___1685450633638247395_70300668607000'
  app/views/pages/index.html.erb:13:in `_app_views_pages_index_html_erb__2084723628308867770_70300687584880'
```

ATP Railties. Opened against master in favor of #10999
Merge pull request #11060 from schneems/schneems/multi-stdout-logging-master

Only output Server logs in Development