tutorial: Use util.promisify()
tutorial: Use util.promisify()

No need to depend on an external dependency thenifyAll, the same
functionality is built into NodeJS.

https://phabricator.endlessm.com/T21578

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib