tns prepare <platform> fails with Unhandled promise rejection

[TsvetanMilanov]

When a plugin has before/after prepare hook which is a promise and it is rejected without error the CLI fails with TypeError: Cannot read property 'stopExecution' of undefined at maybePromise.then (D:\Work\nativescript-cli\lib\common\services\hooks-service.ts:135:28)

Steps to reproduce:

1. tns create test
2. cd test
3. tns plugin add nativescript-fabric@1.0.6
4. tns prepare android