[Test] In test_dynamic_file_system_mounting, check the mounted/unmounted file systems on login nodes.

[gmarciani]

Description of changes

[Test] In test_dynamic_file_system_mounting, check the mounted/unmounted file systems on login nodes.
This test extension is meant to protect us from regression in login nodes update workflow, such as the bug we fixed in aws/aws-parallelcluster-cookbook#3188 where login nodes were not mounting storage when using EFS as internal shared storage.

Tests

ONGOING

test-suites:
  update:
    test_update.py::test_update_slurm:
      dimensions:
        - instances:
            - c5.xlarge
          oss:
            - alinux2023
          regions:
            - us-east-1
    test_update.py::test_dynamic_file_systems_update:
      dimensions:
        - instances:
            - c5.xlarge
          oss:
            - alinux2023
          regions:
            - us-east-1
          schedulers:
            - slurm

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