[6.14.z] variable value should del after update

[Satellite-QE]

Cherrypick of PR: #16969

I extended the existing test case to include the following steps:

1. Create an Ansible variable with a default value and an overridden key.
2. Update the value of the Ansible variable at the host level.
3. After updating, delete the value, ensuring that it reverts to the default value.

Dependent PR: SatelliteQE/airgun#1690

[LadislavVasina1]

Can you please run PRT for all the CP? @amolpati30

[amolpati30]

trigger: test-robottelo
pytest: tests/foreman/ui/test_ansible.py::TestAnsibleCfgMgmt -k test_positive_assign_ansible_role_variable_on_host
airgun: 1688

[amolpati30]

trigger: test-robottelo
pytest: tests/foreman/ui/test_ansible.py::TestAnsibleCfgMgmt -k test_positive_assign_ansible_role_variable_on_host
airgun: 1690

[Satellite-QE]

PRT Result

Build Number: 9731
Build Status: UNSTABLE
PRT Comment: pytest tests/foreman/ui/test_ansible.py::TestAnsibleCfgMgmt -k test_positive_assign_ansible_role_variable_on_host --external-logging
Test Result : ========== 1 failed, 10 deselected, 22 warnings in 771.70s (0:12:51) ===========

[amolpati30]

trigger: test-robottelo
pytest: tests/foreman/ui/test_ansible.py::TestAnsibleCfgMgmt -k test_positive_assign_ansible_role_variable_on_host
airgun: 1690

[Satellite-QE]

PRT Result

Build Number: 9756
Build Status: UNSTABLE
PRT Comment: pytest tests/foreman/ui/test_ansible.py::TestAnsibleCfgMgmt -k test_positive_assign_ansible_role_variable_on_host --external-logging
Test Result : ========== 1 failed, 10 deselected, 22 warnings in 805.70s (0:13:25) ===========

[Gauravtalreja1]

@amolpati30 Auto-cherrypick of dependant airgun PR is failed, could you manually cherrypick it and update this PR?