[QA] Re-add Test::Instance for back-compatibility with GitLab < 11.3

Signed-off-by: Rémy Coutable <remy@rymai.me>

qa/qa.rb

@@ -83,6 +83,7 @@ module QA
     # Test scenario entrypoints.
     #
     module Test
+      autoload :Instance, 'qa/scenario/test/instance'
       module Instance
         autoload :All, 'qa/scenario/test/instance/all'
         autoload :Smoke, 'qa/scenario/test/instance/smoke'

qa/qa/scenario/test/instance.rb

+# frozen_string_literal: true
+
+module QA
+  module Scenario
+    module Test
+      # This class exists for back-compatibility so that gitlab-qa can continue
+      # to call Test::Instance instead of Test::Instance::All until at least
+      # the current latest GitLab version has the Test::Instance::All class.
+      # As of Aug, 22nd 2018. Only GitLab >= 11.3 has this class.
+      module Instance
+        include Bootable
+
+        def self.perform(*args)
+          self.tap do |scenario|
+            yield scenario if block_given?
+            break scenario.do_perform(*args)
+          end
+        end
+
+        def self.do_perform(address, *rspec_options)
+          Runtime::Scenario.define(:gitlab_address, address)
+
+          Specs::Runner.perform do |specs|
+            specs.tty = true
+            specs.options =
+              if rspec_options.any?
+                rspec_options
+              else
+                ::File.expand_path('../specs/features', __dir__)
+              end
+          end
+        end
+      end
+    end
+  end
+end