fix: improve the message when not able to start an emulator so it can be useful for sidekick as well.

[Fatme]

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?

The message that is shown when {N} CLI is not able to start an emulator is not meaningful/useful for sidekick.

What is the new behavior?

The message that is shown when {N} CLI is not able to start an emulator is meaningful/useful for sidekick.