ipatests: do not finalize api when IPA is not configured
    
    Pytest can be executed from a machine that doesn't have IPA configured.
    In this case, api can't be finalized because values such as basedn are
    unknown and missing.
    
    Fixes https://pagure.io/freeipa/issue/7046
    
    Signed-off-by: Tomas Krizek <tkrizek@redhat.com>
    Reviewed-By: Martin Basti <mbasti@redhat.com>