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.

使用 tns run <platform> 重现问题，然后比较当所有设备、模拟器或仿真器断开连接时，tns debug、tns run 和 tns test 如何处理 LiveSync。从命令入口跟踪 LiveSync 操作，并验证错误或所有同步目标的丢失会导致命令退出，而不是继续进行准备工作。