Check SSH connection in ipa-replica-conncheck
    
    Since it is not really possible to separate SSH errors from
    errors of the called program, add a SSH check before
    calling replica-conncheck on the master.
    
    The check also adds the master to a temporary known_hosts file,
    so suppressing SSH's warning about unknown host is no longer
    necessary. If the "real" connection fails despite the check,
    any SSH errors will be included in the output.
    
    https://fedorahosted.org/freeipa/ticket/3402