[AWS] Disable additional auto update services for ubuntu image with cloud-init

[Michaelvll]

Related to #4246

Master:

multitime -n 5 sky launch --cpus 2 --use-spot -y --region us-east-2 --down
===> multitime results
1: sky launch --cpus 2 --use-spot -y --region us-east-2 --down
            Mean        Std.Dev.    Min         Median      Max
real        44.757      2.256       42.070      44.111      48.014      
user        4.977       0.757       4.574       4.605       6.490       
sys         0.482       0.053       0.442       0.454       0.585   

Current:

===> multitime results
1: sky launch --cpus 2 --use-spot -y --region us-east-2 --down
            Mean        Std.Dev.    Min         Median      Max
real        46.844      2.892       43.189      46.732      51.460      
user        4.856       0.579       4.508       4.587       6.013       
sys         0.511       0.070       0.437       0.496       0.645    

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: conda deactivate; bash -i tests/backward_compatibility_tests.sh

[yika-luo]

Thanks @Michaelvll!