[minor] Allow sky check to set enabled_clouds to empty

[Michaelvll]

Tested (run the relevant ones):

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

[concretevitamin]

Hey @Michaelvll could you remind me why this fix is necessary?

[Michaelvll]

Hey @Michaelvll could you remind me why this fix is necessary?

This is to keep the behavior align for the output of sky check and the enabled_clouds in database. In the master, after removing all the cloud credentials and sky check, although it says all clouds are disabled, the enabled_clouds remains unchanged in the database.

It can cause some minor misalignment of the behavior for sky launch. When there was no cloud enabled before, sky launch will fail quickly. If a user removes all their clouds that were enabled and do a sky check, it will show that all the clouds are disabled, but if they sky launch, it will still show the optimizer table instead of failing quickly.

To reproduce on master:

1. sky check having aws enabled
2. mv ~/.aws ~/.aws.bk to disable the aws credential
3. sky check showing AWS being disabled already
4. sky launch will show the optimizer table, instead of just saying there is no cloud enabled.

[cblmemo]

Hey @Michaelvll could you remind me why this fix is necessary?

If the user has one enabled cloud previously and the access token expired, then we should set enabled_clouds to empty instead of keeping this stale record?

[concretevitamin]

Makes sense! LGTM