Defines a new server.

def define(self):
        """Defines a new server."""
        self.server_def = self.consul.define_server(
                self.name,
                self.server_tpl,
                self.server_tpl_rev,
                self.instance_type,
                self.ssh_key_name,
                tags=self.tags,
                availability_zone=self.availability_zone,
                security_groups=self.security_groups,
                **self.provider_extras
                )
        log.debug('Defined server %s' % self.server_def)