Add an ability to avoid rebuilding modules using Angular CLI

Hey guys, I've ran into an issue related to running-time of tests within Angular CLI using Karma runner.
The issue is that every time I'm intended to run the tests Karma rebuilds the modules and it takes so much time.

I'm just wondering whether there's a way to avoid this, like use `ng build` before running tests and provide an ability to use already built modules.

### Expected behaviour
Use already built modules

### Actual behaviour

### Environment Details
*Karma version: 4.0.1*
*NodeJS v8.10.0*
*NPM 6.2.0*

PS - if this kind of question has been raised already - bring me to this please then.