So this error function actually exits the ghost process, making deferring the promise pointless.

I find it weird that we're killing the process here whereas in `./core/index.js` we're just logging an error.

I feel like this is a relic of the old application structure however I want to be sure before it's modified to just reject the promise.

@ErisDS any thoughts as to why here we're quitting the process and [here](https://github.com/TryGhost/Ghost/pull/2225/files#diff-d2ba8c5a9d0c49dbfd1d779891401428R23) we're just logging?