[integ-tests] Add DCV authentication coverage for dotted and long AD usernames

[hanwen-cluster]

Description of changes

Extend the AD integration test to exercise the DCV external authenticator with usernames that contain a "." and that exceed 8 characters, covering the cookbook fix for username validation and UID-based session ownership.

Changes:

• Enable DCV in the AD cluster configs.
• Create additional AD users ("pcluster.user", "pcluster.long.user") that contain a dot and exceed 8 characters.
• After the user workloads, start a DCV session as each of these users and assert the authenticator validates the session for that username.

Refactoring:

• Add tests/common/dcv_common.py with shared helpers to start a DCV session and assert the authenticator accepts it for a given username.

Tests

The following tests have been passed

{%- import 'common.jinja2' as common with context -%}
{{- common.OSS_COMMERCIAL_X86.append("rocky8") or "" -}}
{{- common.OSS_COMMERCIAL_X86.append("rocky9") or "" -}}
---
test-suites:
  ad_integration:
    test_ad_integration.py::test_ad_integration:
      dimensions:
        - regions: [ "ap-southeast-1" ]
          instances: {{ common.INSTANCES_DEFAULT_X86 }}
          oss: [ {{ LUSTRE_OS_X86_0 }}, {{ LUSTRE_OS_X86_2 }}, {{ LUSTRE_OS_X86_4 }}]
          schedulers: ["slurm"]
  dcv:
    test_dcv.py::test_dcv_configuration:
      dimensions:
        # DCV on GPU enabled instance
        - regions: [{{ g4dn_2xlarge_CAPACITY_RESERVATION_2_INSTANCES_1_HOURS_NOPG_DCV_OS_X86_1 }}]
          instances: ["g4dn.2xlarge"]
          oss: [{{ DCV_OS_X86_1 }}]
          schedulers: ["slurm"]
        # DCV on ARM + GPU
        - regions: [{{ g5g_2xlarge_CAPACITY_RESERVATION_2_INSTANCES_1_HOURS_NOPG_DCV_OS_X86_3 }}]
          instances: ["g5g.2xlarge"]
          oss: [{{ DCV_OS_X86_3 }}]
          schedulers: ["slurm"]
    test_dcv.py::test_dcv_with_remote_access:
      dimensions:
        - regions: ["ap-southeast-2"]
          instances: {{ common.INSTANCES_DEFAULT_X86 }}
          oss: [{{ DCV_OS_X86_1 }}]
          schedulers: ["slurm"]

References

• Corresponding cookbook change Allow "." and long usernames in the DCV authenticator aws-parallelcluster-cookbook#3208

Checklist

• Make sure you are pointing to the right branch.
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• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.