Use new LDAPClient constructors
    
    Replace get_ldap_uri() + LDAPClient() with new LDAPClient constructors
    like LDAPClient.from_realm().
    
    Some places now use LDAPI with external bind instead of LDAP with simple
    bind. Although the FQDN *should* resolve to 127.0.0.1 / [::1], there is
    no hard guarantee. The draft
    https://tools.ietf.org/html/draft-west-let-localhost-be-localhost-04#section-5.1
    specifies that applications must verify that the resulting IP is a
    loopback API. LDAPI is always local and a bit more efficient, too.
    
    The simple_bind() method also prevents the caller from sending a
    password over an insecure line.
    
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>