Return N/A when host interface auto speed is unsupported

[monrog2]

APIC 4.2(7u) defines fabricHIfPol.speed as an enum without auto. Filtering on that value returns code 301 (Incorrect filter format for fabricHIfPol.speed, value 'auto' is not valid), causing Host Interface Policy Set to Auto to report an unexpected error.

Return N/A with Current APIC does not support fabricHIfPol.speed="auto". for that specific response. Preserve APIC error details on the existing filter exception so the check can match both code and text; other API failures retain ERROR. The existing query and supported-release findings remain unchanged. Document the compatibility behavior and add regression coverage based on the captured APIC response.

Validation: reproduced the original failure before the fix; 54 affected unit tests pass on Python 3.9.6:

python3 -m pytest -q tests/checks/host_interface_policy_set_speed_check tests/test_icurl.py tests/checks/switch_bootflash_usage_check tests/checks/apic_storage_inode_full_check --log-cli-level=CRITICAL

The tests cover unsupported enum handling, existing PASS/FAIL/MANUAL results and policy-group reporting, unrelated filter errors, missing properties/classes, access errors, server errors, and timeouts. Python 2.7/3.8 and live integration runs were not performed locally.

Upstream CI passed the full Python 2.7 and Python 3.8 test jobs: Pytest run.