compat: Save server's API version in for pre-schema servers
    
    When client comunicates with server that doesn't support 'schema'
    command it needs to determine its api version to be able to use the
    right compat code. Storing information about server version reduces the
    need to call 'env' or 'ping' command only to first time the server is
    contacted.
    
    https://fedorahosted.org/freeipa/ticket/6069
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>