test/Gruntfile.js : Run amber_test_runner directly from grunt via a spawned process.

This 47 line Gruntfile.js  by default will:

1) compiles test/Test.st to test/amber_test_runner.js
2) runs all the tests by executing `node test/amber_test_runner.js` from  a spawned context.

Once amber_test_runner.js can been compiled  `grunt nodetest:all` will run all the tests without a compile.

If can build it with grunt you can execute it without a wrapper.