[k8s] Make node termination robust

[romilbhardwaj]

Makes node termination on k8s more robust by:

1. Having separate try catch blocks for each service
2. Adding retries for transient errors
3. Raising non-404 errors encountered during service deletion

Tested:

• Regular sky launch followed by sky down
• sky down after manually deleting services

[Michaelvll]

Thanks @romilbhardwaj for making this more robust! left some minor changes