Use GSS-SPNEGO if connecting locally
    
    GSS-SPNEGO allows us to negotiate a SASL bind with less roundtrips
    therefore use it when possible.
    
    We only enable it for local connections for now because we only
    recently fixed Cyrus SASL to do proper GSS-SPNEGO negotiation. This
    change means a newer and an older version are not compatible.
    
    Restricting ourselves to the local host prevents issues with
    incompatible services, and it is ok for us as we are only really
    looking for speedups for the local short-lived connections performed
    by the framework. Most other clients have longer lived connections,
    so peformance improvements there are not as important.
    
    Ticket: https://pagure.io/freeipa/issue/6656
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Tomas Krizek <tkrizek@redhat.com>