Swtich feature tests to system tests

[spaghetticode]

After #3552 was merged, it may be a good time to upgrade our integration feature tests to system tests.

Hopefully, the test suite execution time may even improve, as with system tests we don't need to use thedatabase_cleaner gem anymore.

This post may help: https://medium.com/table-xi/a-quick-guide-to-rails-system-tests-in-rspec-b6e9e8a8b5f6

[gonzar11]

I will work on this!