ipatests: Perform a connection test before preparing the client
    
    When the host is down, the preparation of the host fails. This
    produces misleading errors, since the test framework reports that
    the actual command being executed failed, when in fact (in case
    of SSHTransport), the cause of failure was unability to establish
    a SSH session.
    
    https://fedorahosted.org/freeipa/ticket/4132
    
    Reviewed-By: Nathaniel McCallum <npmccallum@redhat.com>