Core: Fix AWS/GCP autostop with new provisioner.

[concretevitamin]

Previously, the regex used is incorrect, causing failures to autostop an AWS cluster that just got updated to use the new provisioner.

Before

git checkout b1d8c9d8
sky launch -c dbg --cloud aws --cpus 4+

git checkout bf336028  # master
sky launch -c dbg --cloud aws --cpus 4+ -i0

Observe failure to autostop in the VM's skylet.log:

..
KeyError: 'head_setup_commands'
E 10-18 05:07:42 events.py:51] AutostopEvent error: Command '['ray', 'down', '-y', '/home/ubuntu/.sky/sky_ray.yml']' returned non-zero exit status 1.
E 10-18 05:07:42 events.py:53] Traceback (most recent call last):
E 10-18 05:07:42 events.py:53]   File "/opt/conda/lib/python3.10/site-packages/sky/skylet/events.py", line 48, in run
E 10-18 05:07:42 events.py:53]     self._run()
E 10-18 05:07:42 events.py:53]   File "/opt/conda/lib/python3.10/site-packages/sky/skylet/events.py", line 122, in _run
E 10-18 05:07:42 events.py:53]     self._stop_cluster(autostop_config)
E 10-18 05:07:42 events.py:53]   File "/opt/conda/lib/python3.10/site-packages/sky/skylet/events.py", line 194, in _stop_cluster
E 10-18 05:07:42 events.py:53]     subprocess.run(
E 10-18 05:07:42 events.py:53]   File "/opt/conda/lib/python3.10/subprocess.py", line 524, in run
E 10-18 05:07:42 events.py:53]     raise CalledProcessError(retcode, process.args,
E 10-18 05:07:42 events.py:53] subprocess.CalledProcessError: Command '['ray', 'down', '-y', '/home/ubuntu/.sky/sky_ray.yml']' returned non-zero exit status 1.
E 10-18 05:07:42 events.py:53]

With this PR

• after running the above, switch to this branch and run

sky launch -c dbg --cloud aws --cpus 4+ -i0

• observe that autostop kicks in correctly

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below): above
• All smoke tests: pytest tests/test_smoke.py
  • pytest tests/test_smoke.py::test_autostop --aws
• 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 identifying and fixing this issue @concretevitamin! Left two comments. We should get this in once the test is passed

[concretevitamin]

Smoke test (autostop) and manual back-compat tests passed. Merging.