Uses Rails transactional tests instead of DatabaseCleaner
transaction strategy because that doesn't work with JS tests

Updates changed method names and fixes spec failures

This allows the BetterErrors REPL to be available
when your GitLab instance is listening on
something _other_ than localhost.

With a recent change in i18n, default language is not
included in fallbacks by default. This causes that
MissingTranslationData exception is raised both in
development and production mode.

This patch sets explicitly fallbacks language to english
which assures that english is used for missing translations.

Fixes rails 5 deprecation warnings in `config/` files

It fixes Rails 5.0 deprecation flooding like:

```
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "::Gitlab::Middleware::ReadOnly" => Gitlab::Middleware::ReadOnly

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "ActionDispatch::Static" => ActionDispatch::Static

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "Gitlab::Testing::RequestBlockerMiddleware" => Gitlab::Testing::RequestBlockerMiddleware

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "ActionDispatch::Static" => ActionDispatch::Static

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "Gitlab::Testing::RequestInspectorMiddleware" => Gitlab::Testing::RequestInspectorMiddleware

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
```

Signed-off-by: Rémy Coutable <remy@rymai.me>

See https://jtway.co/speed-up-your-rails-test-suite-by-6-in-1-line-13fedb869ec4

Adds support for https://gitlab.com/gitlab-com/infrastructure/issues/57

Enabling caching of classes slows start-up time because all controllers
are loaded at initialization, but it reduces memory and load because files
are not reloaded with every request. For example, caching is not necessary
for loading database migrations but useful for handling Knapsack specs.

Addresses gitlab-org/gitlab-ee#2162

The idea is that after each feature spec example, we block all incoming
requests at the Rack level, go to the 'about:blank' page, and wait until
the current requests reach 0.

This should solve the problem where a request would end after database
cleaner performed the database truncation. The problem was that a GET
request can still lead to records creation (e.g. namespaces or routes).

Signed-off-by: Rémy Coutable <remy@rymai.me>

[ci skip]

quiet_assets has been seemingly abandoned, and now sprockets-rails has the feature built-in!

From this PR: https://github.com/rails/sprockets-rails/pull/355

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb