Shows an appropriate message while trying to run the app in a non-project folder

[jamesgeorge007]

Shows up an appropriate message while trying to run app in non-project directory

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

If you try to run app in non-project folder with --path in command without existing folder, you will see exception and you couldn't understand what is the problem.

What is the new behavior?

correct error for non existing folder

Closes #4280

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[jamesgeorge007]

@Fatme Thoughts?

[Fatme]

test cli-smoke