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
This cleanup aims to fix a build failure:
https://travis-ci.org/rails/rails/jobs/3515951/#L482
Since travis always have both ENV vars set to "test", a test is failing
where it's expected to output the default env "development", but "test"
is the result due to RACK_ENV being set when we expect it to not be.
By cleaning this duplication we ensure that changing any of these env
variables will pick the right expected value.
When launching rails server from the command line with a rails environment specified such as `rails server RAILS_ENV=production` an error would occur since rails will try to use `RAILS_ENV=production` as it's server.
When launching rails with a specified server such as thin `rails server thin RAILS_ENV=production` no error will be thrown, but rails will not start up in the specified environment.
This fixes both of those cases
