I find existing VMs that are already running that might be orphaned instances of this worker.

def _find_existing_instance(self):
        """
        I find existing VMs that are already running that might be orphaned instances of this worker.
        """
        if not self.connection:
            return None

        domains = yield self.connection.all()
        for d in domains:
            name = yield d.name()
            if name.startswith(self.workername):
                self.domain = d
                break

        self.ready = True