[6.15.z] Fix Discovery Tests

[Satellite-QE]

Cherrypick of PR: #16605

Problem Statement

Discovery tests were failing with hussh backend as the shell didn't have stdout attribute and also because of a bug in hussh: JacobCallahan/Hussh#26

Solution

Updated the tests to exit the shell contextmanager and read shell.result.stdout. Also, because of the bug, we need to explicitly close the shell before exiting contextmanager.

Related Issues

[Satellite-QE]

trigger: test-robottelo
pytest: tests/foreman/api/test_discoveredhost.py --external-logging --include-onprem-provisioning -m on_premises_provisioning
provisioning: true
env:
    ROBOTTELO_server__deploy_arguments__deploy_rhel_version: '9'
    ROBOTTELO_server__deploy_arguments__deploy_sat_version: '6.16'
    ROBOTTELO_server__deploy_arguments__deploy_snap_version: '9.0'
    BROKER_SSH_BACKEND: hussh

[Satellite-QE]

PRT Result

Build Number: 9352
Build Status: UNSTABLE
PRT Comment: pytest tests/foreman/api/test_discoveredhost.py --external-logging --include-onprem-provisioning -m on_premises_provisioning --external-logging --include-onprem-provisioning
Test Result : ===== 9 passed, 5 deselected, 1185 warnings, 1 error in 6081.11s (1:41:21) =====