text: Title: [Core/UX] Improve the display of returncode for multi-node
  Body: <!-- Describe the bug report / feature request here -->
  
  When a user's job is running on multiple nodes and one node fails with a return code, e.g. 1, SkyPilot will kill the processes on the other nodes, with a return code 137. It is confusing to users to see a list of return code like the following: `ERROR: Job 1 failed with return code list: [1, 137, 137]`
  
  Instead, we should show message like the following:
  ```
  ERROR: Job 1 failed with returncode: 1 on one node worker-2, SkyPilot cleaned the processes on other nodes with returncode 137
  ```
  
  <!-- If relevant, fill in versioning info to help us troubleshoot -->
  _Version & Commit info:_
  * `sky -v`: PLEASE_FILL_IN
  * `sky -c`: PLEASE_FILL_IN
  