This commit adds the RailsMultisite middleware in test mode when Rails.configuration.multisite is true. This allows for much more realistic integration testing. The `multisite_spec.rb` file is rewritten to avoid needing to simulate a middleware stack.
Mixing multisite and standard specs can lead to issues (e.g. when using `fab!`)
Disabled the (upcoming https://github.com/discourse/rubocop-discourse/pull/11) rubocop rule for two files that have thoroughly tangled both types of specs.
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
