parallel.rb: fix intervention

* test/lib/test/unit/parallel.rb (_report): send a response and a
  newline atomically, to get rid of intervention with "p" which
  runs in a separate thread.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57589 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/lib/test/unit/parallel.rb

@@ -152,8 +152,7 @@ module Test
       end
 
       def _report(res, *args) # :nodoc:
-        res = "#{res} #{args.pack("m0")}" unless args.empty?
-        @stdout.puts(res)
+        @stdout.write(args.empty? ? "#{res}\n" : "#{res} #{args.pack("m0")}\n")
       end
 
       def puke(klass, meth, e) # :nodoc: