Support run extension's test case with hphp/test/run

Currently built-in extension's unit test are located in hhvm codebase, but the opensourced
extension mostly use phpunit, but I 
think use `hphp/test/run` to test makes it more consistent, it can be the standard way
to do unit test of HHVM extension.

Now hhvm-dev package should contain hphp/test/run,
after running `hphpize`,  `run` will copied to extension dir and renamed to `run-test`.

User can run `make test` to run tests under folder `test`, currently
it can only be in `test` folder