ipatests: fix expected errmsg in TestTrust::test_ipa_commands_run_as_aduser
    
    389ds does not return any more additional information
    about a failing bind (to avoid leaking information).
    
    As a consequence, when ipa ping is executed with an AD user
    the error message contains less info as in the past and needs to be fixed.
    
    Fixes: https://pagure.io/freeipa/issue/8668
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Sergey Orlov <sorlov@redhat.com>