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

lib/autospec/simple_runner.rb

@@ -16,18 +16,17 @@ module Autospec
         self.abort
       end
       # we use our custom rspec formatter
-      args = ["-r", "#{File.dirname(__FILE__)}/formatter.rb"]
+      args = [
+        "-r", "#{File.dirname(__FILE__)}/formatter.rb",
+        "-f", "Autospec::Formatter"
+      ]
 
       command = begin
-        if ENV["PARALLEL_SPEC"] &&
+        if ENV["PARALLEL_SPEC"] != '0' &&
               !specs.split.any? { |s| puts s; s =~ /\:/ } # Parallel spec can't run specific groups
 
-          args += ["-f", "progress", "-f", "Autospec::ParallelFormatter", "-o", "./tmp/rspec_result"]
-          args += ["-f", "ParallelTests::RSpec::RuntimeLogger", "-o", "./tmp/parallel_runtime_rspec.log"] if specs == "spec"
-
-          "parallel_rspec -- #{args.join(" ")} -- #{specs.split.join(" ")}"
+          "bin/turbo_rspec #{args.join(" ")} #{specs.split.join(" ")}"
         else
-          args += ["-f", "Autospec::Formatter"]
           "bin/rspec #{args.join(" ")} #{specs.split.join(" ")}"
         end
       end