[INFR-1207] add rakefile

[aks]

This PR:

• adds a Rakefile, with the default rule being set to run "spec".
• fixes some flaky tests

Running rspec requires that the file spec/rails_helper.rb exist (even if it's empty).

Since the target app is a rails app, when using rspec, it appears that it is necessary to declare both "rails" and "railties" as dependencies in the perf_check gemspec, or tests won't pass consistently.

Also added the "fuubar" gem which makes rspec progress reporting more informative and pleasant.

Testing

• [ ] pull this branch and cd to the directory
• [ ] run bundle install to make sure all the proper gems are installed
• [ ] run bundle exec rake -T and see the possible rake tasks
• [ ] run bundle exec rake spec and watch the tests pass/skip

[aks]

@sudara -- this test is failing on travis, but does not fail on my system. Can you please check this out?

Also, would be helpful if the Travis testing spit out the random seed so we can replicate failed Travis tests.