[GCP][Disk] `sky launch --cpus 2 --cloud gcp --disk-tier ultra` not showing real reason

[cblmemo]

Introduced in #3935. The logging for sky launch --disk-tier ultra --cpus 2 --cloud gcp is super confusing, as it does not actually show the reason why we cannot launch the instance on GCP, which is all instance types with 2 vCPUs is not supported by the pd-extreme disk.

sky launch --cpus 2 --cloud gcp --disk-tier ultra
I 09-13 01:05:04 optimizer.py:1301] No resource satisfying GCP(cpus=2, disk_tier=ultra) on GCP.
sky.exceptions.ResourcesUnavailableError: Catalog does not contain any instances satisfying the request:
Task<name=sky-cmd>(run=<empty>)
  resources: GCP(cpus=2, disk_tier=ultra).

To fix: relax or change the resource requirements.

Hint: sky show-gpus to list available accelerators.
      sky check to check the enabled clouds.

Version & Commit info:

• sky -v: PLEASE_FILL_IN
• sky -c: PLEASE_FILL_IN

[Michaelvll]

Related to #3911

[github-actions[bot]]

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