pwpolicy: Fix tests for 'minlength: ""'

When clearing minimum length parameter, FreeIPA raises an error, and the
error is different when executing the playbook in server or client
context. Since the error message is evaluated in the text, both errors
must be accepted as "not a failure", since ansible-freeipa did the
correct call.

Once https://pagure.io/freeipa/issue/9297 is fixed, the test must be
updated to not accept any of these error messages.