Search and run venus tests automatically

I make the `run` command to search and run venus tests if test file is not given.

I put a root-directory option in `run` command to give the possibility of set the root dir to start the search.

**plus**: I added to contributing docs the node packages needed to run venus tests with `npm test`

**ps**: I don't know how to create a test to init method of executor.js. If you give me a way to create the tests, I do it and make another pull request :+1: