[integ-tests-framework] Fix failures from instance type reservation

[hanwen-cluster]

Description of changes

• Make resolve_default_instance compatible with tests without instance fixture
• Skip p series instance types in resolve_default_instance

See commit descriptions for details

Tests

The following tests have passed or skipped as expected:

test-suites:
  efa:
    test_efa.py::test_efa:
      dimensions:
      - instances:
        - p6-b200.48xlarge
        oss:
        - rhel9
        regions:
        - us-east-2
        schedulers:
        - slurm
      - instances:
        - p6-b200.48xlarge
        oss:
        - ubuntu2204
        regions:
        - us-east-2
        schedulers:
        - slurm
      - instances:
        - p6-b200.48xlarge
        oss:
        - rocky8
        regions:
        - us-east-2
        schedulers:
        - slurm
      - instances:
        - p6-b200.48xlarge
        oss:
        - rhel8
        regions:
        - us-east-2
        schedulers:
        - slurm
      - instances:
        - p6-b200.48xlarge
        oss:
        - alinux2023
        regions:
        - us-east-2
        schedulers:
        - slurm
      - instances:
        - p6-b200.48xlarge
        oss:
        - ubuntu2404
        regions:
        - us-east-2
        schedulers:
        - slurm
  networking:
    test_networking.py::test_public_network_topology:
      dimensions:
      - regions:
        - af-south-1
    test_networking.py::test_public_private_network_topology:
      dimensions:
      - regions:
        - af-south-1
  pcluster_api:
    test_api_infrastructure.py::test_api_infrastructure_with_default_parameters:
      dimensions:
      - regions:
        - ap-south-1
    test_api_infrastructure.py::test_api_infrastructure_with_full_parameters:
      dimensions:
      - regions:
        - eu-west-1

References

• Link to impacted open issues.
• Link to related PRs in other packages (i.e. cookbook, node).
• Link to documentation useful to understand the changes.

Checklist

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