fix(ios): check if there are any available simulators or physical devices

[szymonrybczak]

Summary:

In this PR I added condition which check if there are any simulators / physical devices available.

Test Plan:

1. Clone the repository and do all the required steps from the Contributing guide
2. Uninstall simulators and unpair physical devices
3. Command xcrun xcdevice list should list only your computer
4. Run this command:

node /path/to/react-native-cli/packages/cli/build/bin.js run-ios

It should give an error.

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[szymonrybczak]

Tests passing locally, changes not related to failure. I don't know why recently there's so much flakiness problems around these E2E tests.