test_ldap: drop redundant URI argument
    
    Use the default LDAP URI from api.env.ldap_uri instead of specifying a
    custom URI in the argument. The default URI might be ldapi://, so make sure
    autobind is not attempted where the custom URI was ldap://.
    
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>