Wait for the new file modal to stop animating before clicking it

We now need to click the commit button 3 times:
1. To enter commit mode
2. To being staging changes
3. To submit the commit

Add knapsack qa report and use it to run tests in parallel

Use the RSpec runner with knapsack

The way the Knapsack runner uses exec to start rspec seems
incompatible with the way we expect it to work. Plus, it requires
specifying KNAPSACK_TEST_DIR.

Instead, we use knapsacks AllocatorBuilder to select the spec
files to run, and then start rspec as normal, via
RSpec::Core::Runner.run

This also means we can incorporate tags.

Let the job run automatically

Include KNAPSACK_TEST_FILE_PATTERN in vars

Check all defined knapsack env vars before requiring knapsack

Elements now have the ability to be required on pages or not
Currently using the default wait mechanism
Altered the ElementWithPattern Cop to fit new splat for init

No need to retry automatically when running tests locally

Fix E2E test - wait for branches to not be present

See merge request gitlab-org/gitlab-ce!27805

Uses the branch_name element to find a branch with a specific
name, instead of using a dynamic CSS class that can't be validated
by the sanity selector test

Add frozen_string_literal to qa/

See merge request gitlab-org/gitlab-ce!27266

This will be default in Ruby 3, so will be good to apply in QA ahead of
time to be consistent.