Don't fight against ourselves for the default log level

If we want to always default to :debug, let's just do that.

At which point the production.rb entry can become an "uncomment to
change" instead.
Replacing an each with reduce

The functionality has not changed, but the code is more elegant by
using `reduce` instead of `each`.

This way no accumulator needs to be declared, no explicit return is
needed.
Using `each_with_object` instead of `reduce`

This way no new object allocation is taking place. Thanks @jeremy for
the suggestion!
Merge pull request #16626 from adomokos/replacing-each-with-reduce

Replacing an each with reduce
Merge pull request #16622 from matthewd/default-debug

Don't fight against ourselves for the default log level
Use system /tmp when testing actionpack

Fixes rails/rails-dev-box#76 since DRb cannot connect to a socket inside Vagrant's synced folder