def start(self):
        """Start the ssh client and connect to the host.

        It will wait until the ssh service is available during 90 seconds.
        If it doesn't succed to connect then the function will raise
        an SSHException.
        """
        if self.via_ip:
            connect_to = self.via_ip
            self.description = '[%s@%s via %s]' % (self._user,
                                                   self._hostname,
                                                   self.via_ip)
        else:
            connect_to = self._hostname
            self.description = '[%s@%s]' % (self._user,
                                            self._hostname)

        exception = None
        for i in range(60):
            try:
                self._client.connect(
                    connect_to,
                    username=self._user,
                    allow_agent=True,
                    key_filename=self._key_filename)
            # NOTE(Gonéri): TypeError is in the list because of
            # https://github.com/paramiko/paramiko/issues/615
                self._transport = self._get_transport()
            except (OSError,
                    TypeError,
                    ssh_exception.SSHException,
                    ssh_exception.NoValidConnectionsError) as e:
                exception = e
                LOG.info('%s waiting for %s: %s' %
                         (self.description, connect_to, str(exception)))
                time.sleep(1)
            else:
                LOG.debug('%s connected' % self.description)
                self._started = True
                return

        _error = ("unable to connect to ssh service on '%s': %s" %
                  (self._hostname, str(exception)))
        LOG.error(_error)
        raise exception
Start the ssh client and connect to the host.

        It will wait until the ssh service is available during 90 seconds.
        If it doesn't succed to connect then the function will raise
        an SSHException.