Fixed a flaky test

[suzzy777]

What is the purpose of the change:

• This PR is to fix a flaky test tests/test_api.py::TestAPI::test_missing_agent, which can fail after running any of the 9 polluters :

1. tests/test_execute.py::TestExecute::test_valid_execute
2. tests/test_get_attribute.py::TestGetAttribute::test_valid_bulk_request
3. tests/test_get_attribute.py::TestGetAttribute::test_valid_request
4. tests/test_list.py::TestList::test_invalid_path
5. tests/test_list.py::TestList::test_valid_request
6. tests/test_search.py::TestSearch::test_valid_search
7. tests/test_set_attribute.py::TestSetAttribute::test_valid_bulk_write
8. tests/test_set_attribute.py::TestSetAttribute::test_valid_request
9. tests/test_version.py::TestVersion::test_valid_version, but passes when it is run in isolation.

Reproduce the test failure:

• Run the following command:
  python -m pytest tests/test_execute.py::TestExecute::test_valid_execute tests/test_api.py::TestAPI::test_missing_agent
• This command can be used with all (9) of the above mentioned polluters and the order dependent test - tests/test_api.py::TestAPI::test_missing_agent

Expected Result:

• Test tests/test_api.py::TestAPI::test_missing_agent should pass when run after test tests/test_execute.py::TestExecute::test_valid_execute or any of the other 9 polluters.

Actual Result:

• Test tests/test_api.py::TestAPI::test_missing_agent fails when it is run after any of the polluters.

Why the test fails:

• The flaky test fails because the test is dependent on some state that's being changed by the polluters.

Fix:

• The changes in this pull request cleans the state polluted by the polluter and makes the flaky test pass.