fix generated mtest

mtest doesn't always return a nonzero status code, so we need to check
the output for failure conditions.

Author: hone

bintest/mruby-cli.rb

@@ -40,6 +40,8 @@
 
         output, status = Open3.capture2("rake test:mtest")
         assert_true status.success?, "Process did not exit cleanly"
+        assert_false output.include?("Error:"), "mtest has errors"
+        assert_false output.include?("Failure:"), "mtest has failures"
       end
     end
   end

mrblib/setup.rb

@@ -63,7 +63,7 @@ def test
       <<TEST
 class Test#{Util.camelize(@name)} < MTest::Unit::TestCase
   def test_main
-    assert_nil __main__
+    assert_nil __main__([])
   end
 end