Fix multi user tests

The tests test_users_present.yml and test_users_absent.yml has been
merged into test_users_present_absent.yml to fix the independent test
order execution.

The test test_users_present_slice.yml has been renamed to
test_users_present_absent_slice.yml.

Both tests are cleaning up possible exiting entries before running the tests
and are verifying the present and absent task result.