Use protractor api instead of `npm run e2e` in `ng e2e`

[filipesilva]

When running ng e2e we just call npm run e2e. We should use the protractor API instead since it gives us better control over output and config.

A similar move was done for lint in #4248.

[hansl]

Reminder to implement an npm script "e2e": "ng e2e".