Merge branch 'tc-geo-test-rake-tasks' into 'master'

Memoize migration files per migrations paths

Closes #3701

See merge request gitlab-org/gitlab-ee!3147

config/initializers/ar_speed_up_migration_checking.rb

@@ -10,7 +10,8 @@ if Rails.env.test?
         # it reads + parses `db/migrate/*` each time. Memoizing it can save 0.5
         # seconds per spec.
         def migrations(paths)
-          (@migrations ||= migrations_unmemoized(paths)).dup
+          @migrations ||= {}
+          (@migrations[paths] ||= migrations_unmemoized(paths)).dup
         end
       end
     end