:param tags:list of tags you to connect to (tagname=value)
        :return: instance list

def get_instances_by_tag(self, tags):
        """
        :param tags:list of tags you to connect to (tagname=value)
        :return: instance list
        """

        try:
            c = ec2.connect_to_region(self._region,
                                      aws_access_key_id=self._aws_access_key_id,
                                      aws_secret_access_key=self._aws_secret_access_key)

            # select instance by list of tags (OR used)
            reservations = c.get_all_reservations(filters=SergentSsh.tags_to_dict(tags))
            instances = list()

            for r in reservations:
                # for each instance launched by this reservation
                for instance in r.instances:
                    # we need only running instances
                    if instance.state.lower() == 'running':
                        instances.append(instance)

            return instances
        except NoAuthHandlerFound:
            raise SergentSshException('Boto said that you should check your credentials')