react-native init task should use run-windows

[jonthysell]

The react-native init task in out CLI should use run-windows to confirm that works.

Correspondingly, we might not need to use run-windows elsewhere in the CI (like SampleApps)

[chrisglein]

We should decide whether we want it to boot the app (to validate that it works) versus not. May need an option to run-windows to do the build but not launch (if one doesn't exist already)