DEV: Add a new way to run specs in parallel with better output (#7778)

* DEV: Add a new way to run specs in parallel with better output

This commit:

 1. adds a new executable, `bin/interleaved_rspec` which works much like
    `rspec`, but runs the tests in parallel.

 2. adds a rake task, `rake interleaved:spec` which runs the whole test
    suite.

 3. makes autospec use this new wrapper by default. You can disable this
    by running `PARALLEL_SPEC=0 rake autospec`.

It works much like the `parallel_tests` gem (and relies on it), but
makes each subprocess use a machine-readable formatter and parses this
output in order to provide a better overall summary.

(It's called interleaved, because parallel was taken and naming is
hard).

* Make popen3 invocation safer

* Use FileUtils instead of shelling out

* DRY up reporter

* Moved summary logic into Reporter

* s/interleaved/turbo/g

* Move Reporter into its own file

* Moved run into its own class

* Moved Runner into its own file

* Move JsonRowsFormatter under TurboTests

* Join on threads at the end

* Acted on feedback from eviltrout

config/boot.rb

@@ -33,16 +33,21 @@ end
 
 # Parallel spec system
 if ENV['RAILS_ENV'] == "test" && ENV['TEST_ENV_NUMBER']
-  n = ENV['TEST_ENV_NUMBER'].to_i
+  if ENV['TEST_ENV_NUMBER'] == ''
+    n = 1
+  else
+    n = ENV['TEST_ENV_NUMBER'].to_i
+  end
+
   port = 10000 + n
 
-  puts "Setting up parallel test mode - starting Redis #{n} on port #{port}"
+  STDERR.puts "Setting up parallel test mode - starting Redis #{n} on port #{port}"
 
   `rm -rf tmp/test_data_#{n} && mkdir -p tmp/test_data_#{n}/redis`
   pid = Process.spawn("redis-server --dir tmp/test_data_#{n}/redis --port #{port}", out: "/dev/null")
 
   ENV["DISCOURSE_REDIS_PORT"] = port.to_s
-  ENV["RAILS_DB"] = "discourse_test_#{ENV['TEST_ENV_NUMBER']}"
+  ENV["RAILS_DB"] = "discourse_test_#{n}"
 
-  at_exit { puts "Terminating redis #{n}"; Process.kill("SIGTERM", pid); Process.wait }
+  at_exit { STDERR.puts "Terminating redis #{n}"; Process.kill("SIGTERM", pid); Process.wait }
 end