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

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

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>