Don't load test env by default

After those two commits
999835a8e5a34afb41af54f3cb14562a6c759a04
58476a7a936e05bef0a767dc14b404c8a230a15b

default env in usual rails application (where `rails/all` is used) for `bundle exec rake -T` command became `test`.

This is confusing at least for me (I was sure that `development` env is default) and leads to "strange" errors in some applications.

cc @tenderlove