UX: if a cluster becomes INIT, warn about autostop reset.

[concretevitamin]

User reported that it's confusing an newly-INIT (abnormal) cluster suddenly had its autostop canceled.

This PR adds a warning when that happens.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)

sky launch -c dbg -i10
# ssh into dbg and `ray stop`
sky status -r  # Observed warning.

• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Backward compatibility tests: bash tests/backward_comaptibility_tests.sh

[Michaelvll]

Thanks for adding this hint @concretevitamin! Left two nits.

[Michaelvll]

LGTM. Thanks!