LiveSync related commands hang when devices for sync are disconnected

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: 5.3.0
• Cross-platform modules: Not applicable
• Android Runtime: Not applicable
• iOS Runtime: Not applicable
• Plugin(s):Not applicable

Describe the bug
Whenever all devices/emulators/simulators that we are using for LiveSync operation are disconnected or CLI is unable to sync changes on them, the command (tns debug, tns run, tns test...) should exit. Instead, it continues its execution and prepares the application.

To Reproduce

1. Run tns run <platform>
2. When the operation is running, disconnect all devices/stop all emulators/simulators on which you are syncing.
3. Command should exit.
   Instead it continues its execution.

Expected behavior
Once all devices used for liveSync are disconnected (or we have errors when trying to sync on them), command should exit and does not give incorrect impression that it still liveSyncs your project.

tns run <platform> で再現し、その後、すべてのデバイス、エミュレーター、またはシミュレーターが切断された場合に、tns debug、tns run、tns test が LiveSync をどのように処理するかを比較します。コマンドのエントリーポイントから LiveSync の処理を追跡し、エラーまたはすべての同期対象の喪失によって、準備を続行するのではなくコマンドが終了することを確認します。