capybara/rspec already calls Capybara.reset_sessions! in an
`after` hook, but `block_and_wait_for_requests_complete` is called
before it so by calling it explicitely here, we prevent any new
requests from being fired.
See
https://github.com/teamcapybara/capybara/blob/ffb41cfad620de1961bb49b1562a9fa9b28c0903/lib/capybara/rspec.rb#L20-L25Signed-off-by: NRémy Coutable <remy@rymai.me>

This change fix a memory leak due to a Webkit bug:
https://github.com/ariya/phantomjs/issues/12903

Also:

- Whitelist only localhost and 127.0.0.1 in Capybara + JS specs
- Blacklist all requests to media such as images, videos, PDFs, CSVs etc.
- Log all the requests made.
Signed-off-by: NRémy Coutable <remy@rymai.me>

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

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

Also disabled assets warming for Capybara/RSpec and remove a check to
skip assets warming when ./tmp/cache/assets/test exists because assets
are now served by webpack-dev-server.
Signed-off-by: NRémy Coutable <remy@rymai.me>

We were unintentionally hitting `gravatar.com` whenever a test that used
Poltergeist was run. This was certainly wasting their resources and
slowing down our tests even further, for no reason.

The problem occurred because asset compilation takes a long time, so
when the asset cache didn't exist and the first test ran, it would often
(randomly) time out during the generation before the actual test even
had a chance to run.

Now we check if the cache exists before the suite runs, and if not, we
manually fire a request to the root URL in order to generate it. This
should allow subsequent tests to use the cached assets.

In case we end up wanting to use it in Spinach as well.

Also adds capybara-screenshot, which will automatically save the page as
html and an image whenever a feature fails. Handy for debugging.