mrbtest using tools/mruby


 - `cat test/t/*.rb > build/host/test/mrbtest.rb`
 - `mrbc build/host/test/mrbtest.rb`
 - `./bin/mruby build/host/test/mrbtest.rb`
 - `./bin/mruby -b build/host/test/mrbtest.mrb`

```
$ rake test
>>> Test host <<<
mrbtest - Embeddable Ruby Test

This is a very early version, please test and report errors.
Thanks :)

........................ (snip) ........................
Total: 516
   OK: 516
   KO: 0
Crash: 0
 Time: 0.614565 seconds

*** Test with tools/mruby (rb file) ***
Success

*** Test with tools/mruby (mrb file) ***
Success

```