CLI does not detect invalid platforms folder content

[DimitarTachev]

Reported by: @MartoYankov

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 6.2.1
• Cross-platform modules: 6.2.0
• Android Runtime: 6.2.0
• iOS Runtime: 6.2.0

Describe the bug

To Reproduce

1. tns create newApp --js
2. rm -rf platforms
3. mkdir -p platforms/android
4. tns run android
5. Unable to apply changes on device: emulator-5554. Error is: spawn ./gradlew ENOENT. will be thrown.

Expected behavior
The CLI should detect the invalid platforms state and suggest something like rm -rf platforms and npm cache clean --force.

Additional context
The invalid folder should be also handled for iOS and cloud builds.