Returns the uBridge hypervisor.

        :returns: instance of uBridge

def ubridge(self):
        """
        Returns the uBridge hypervisor.

        :returns: instance of uBridge
        """

        if self._ubridge_hypervisor and not self._ubridge_hypervisor.is_running():
            self._ubridge_hypervisor = None
        return self._ubridge_hypervisor