[autoscaler][aws] Refactor _check_ami to work with available node types

[DmitriGekhtman]

What is the problem?

Ray version and other system information (Python version, TensorFlow version, OS):

Subset of
#15108

This makes ray up aws/example-full.yaml fail with AWS accounts based in certain (most?) regions.
See this discussion:
https://discuss.ray.io/t/cannot-copy-ami-ami-0a2363a9cff180a64/1720

Reproduction (REQUIRED)

Please provide a short code snippet (less than 50 lines if possible) that can be copy-pasted to reproduce the issue. The snippet should have no external library dependencies (i.e., use fake or mock data / environments):

If the code snippet cannot be run by itself, the issue will be closed with "needs-repro-script".

• I have verified my script runs in a clean environment and reproduces the issue.
• I have verified the issue also occurs with the latest wheels.

[DmitriGekhtman]

Actually, maybe part of the the right fix here would be to change ImageId in our example configs to latest_dlami which is autofilled to the right thing.