Improving app and mocking for e2e tests

[danielherrerohernando]

What’s the focus of this PR

This PR adds basic greeting functionality to index.js and mocking for handling child process when running integration/e2e tests. I don´t like having test stuff inside "production" index.js but I don´t know any other way of mocking a child process function like 'getCurrentHour'. Suggestions accepted.

How to review this PR

Check IPC(https://medium.com/@NorbertdeLangen/communicating-between-nodejs-processes-4e68be42b917) approach for mocking time.

Before submitting this PR, I made sure:

• [x] The code builds clean without any errors or warnings

[danielherrerohernando]

This PR is extended by #8